High-density illumination system

ABSTRACT

A compact and efficient optical illumination system featuring planar multi-layered LED light source arrays concentrating their polarized or un-polarized output within a limited angular range. The optical system manipulates light emitted by a planar array of electrically-interconnected LED chips positioned within the input apertures of a corresponding array of shaped metallic reflecting bins using at least one of elevated prismatic films, polarization converting films, micro-lens arrays and external hemispherical or ellipsoidal reflecting elements. Practical applications of the LED array illumination systems include compact LCD or DMD video image projectors, as well as general lighting, automotive lighting, and LCD backlighting.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application is a Non-Provisional of U.S. Application60/442,624 filed Jan. 24, 2003, incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

[0002] The present invention, which is an expansion on inventionsdescribed in a previously filed application, entitled UniformIllumination System filed on Dec. 14, 2001, Ser. No. 10/31,980C, andwhich is incorporated by reference herein, is concerned generally with athin and compact multi-layered optical system and method for generatingwell-organized output illumination from a one or two-dimensional arrayof discrete light emitting diodes (LEDs), the output light spreaduniformly over the system's aperture while emanating from a uniquelymulti-layered system comprised of reflecting bins and elevated lightdirecting films. The present invention focuses centrally on thebeneficial interactions between the geometric parameters of a thin arrayof metallically-reflecting bins, each having four tapered sidewallsmeeting at an input aperture containing an LED, and the geometricparameters of orthogonally oriented prism sheets (and/or polarizationconverting sheets) placed above them. The previous invention describedthe basic geometric configurations of such multi-layers, while thepresent invention explores their performance differences, and in doingso, sets forth two specific embodiments related to directed LED lightingand illumination, as well as adding means for additional efficiencygains by the external recycling of otherwise wasted light. The first LEDlight source array embodiment trades optical efficiency to achieveoutput beams having the highest practical density of lumens, making veryhigh-power illumination applications such as occur in video projectorspractical at the soonest opportunity. In this non-etendue-preservingembodiment, interactions between reflecting bins and elevated prismsheets, polarization-converting films and/or micro-lens arrays causebeneficial spatial overlap of bin outputs that increase the array'seffective lumen density. The second LED light source array embodimentachieves highest possible optical efficiency, allowing high-brightnessillumination applications using the fewest possible LEDs and/or thelowest amounts of electrical power. In this etendue-preservingembodiment, shaped reflecting bins are combined with elevatedmicro-lenses and polarization converting films to manipulate theillumination pattern especially for square or rectangular illuminationtargets. Accordingly, the field of illumination produced by theparticular optical systems containing these multi-layered emittingarrays provide a suitable illuminating beam for projecting an electronicimage (as from an LCD or DMD) onto a screen, or the illumination itselfcomposed of separately-controlled image pixels, the sum of which at anyinstant forming a spatially modulated image to be viewed directly, as inLED image displays for signage and video. The field of directedillumination may also be used as a means of general illumination, as inlighting fixtures and luminaries. More particularly, the multi-layeroptical system that achieves this favorable performance consists of aheat extraction layer, an electronic back plane containing a regular oneor two-dimensional array of electronically interconnected LEDs(preferably flip-chip style), an micro-fabricated array of contiguous(or nearly contiguous) reflecting bins with shaped or plane taperedsidewalls, one bin surrounding each LED (or group of LEDs), and asequence of at least one additional optical light directing layerpositioned above or at a preferred spacing from the reflecting binapertures, the layer construction designed in conjunction with thegeometry of the underlying reflecting bins, so as to maximize the lightsource array's output power and field coverage within a particularangular range, or within a particular angular range and polarizationstate. An additional layer or layers, in configurations that needingsome additional diffusive mixing, can be conventional light spreadingmaterials such as holographic diffusers, lenticular diffusers, lensarrays, bulk or surface scattering diffusers, opal glass, or groundglass, added to improve spatial uniformity.

[0003] Currently available illumination systems capable of achievingequivalent brightness uniformity (and lumen density) using onlyconventional optical elements, do so with at least 2 times fewer lumensper square millimeter, less efficiently (in terms of brightness), and inconsiderably thicker and less well-integrated packaging structures.Currently available LED illumination systems use arrays of discretelypackaged LED devices, or LED chips on interconnection planes disposedbelow conventional refractive optical elements (whose effective opticalcollection range is limited). By comparison, the uniqueness of thepresent invention relates to the fact that its compartmentalizedpackaging layer and its cooperatively designed optical over-layers areboth made to be continuous elements for the entire array—and whosechoice of materials and their geometry achieves significantly enhancedperformance. Designing the reflecting bins and the optical layers abovethem interactively, and by means of a realistic and experimentallyvalidated computer model, is found to maximize optical output comparedwith more conventional designs. The increase in the performance of suchLED light source arrays is not an obvious step despite previous use ofLEDs in arrays, in reflective packages, and in conjunction with manytypes of conventional secondary optical elements.

[0004] Such compact LED illumination systems are of primary interest forthe projection of images onto screens from such spatial light modulatorsas reflective and transmissive LCDs and DMDs. LED illumination isconsidered superior to the commonly used discharge lamps with regard tooperating lifetime, which increases nearly 100-fold, and also becausethe conductive heat generated in the LEDs is easier to extract than theradiative heat given off by a gas discharge. Using LEDs in place ofshort-arc discharge lamps, however, is not straightforward for severalreasons. Discharge lamps generate 60 (white) lumens per watt at 130-150watts, and today's projection systems have rather low end-to-end opticalefficiencies in the range of 15% and less. Imagining the use of today'sbest high-power LEDs at light levels of 7000 to 9000 lumens seems quitedifficult, given that best emission efficacies are only in the range ofonly 15-25 lumens per watt. What's more, manufacturing economies keeptypical LCD and DMD image apertures less than 1.2″ on the diagonal, andsuch devices cannot make effective use of light at angles above ±12degrees. This means that the total effective illumination area for the±90 degree emitting LEDs has to be less than 19.28 mm², or for thestandard image 4:3 aspect ratio, less than a rectangular area 5.07 mm by3.80 mm. While such jumbo chips might become available in the distantfuture, the largest chips known today are square and not yet larger than1 mm or 2 mm on an edge (as manufactured by LumiLeds, San Jose, Calif.).Even were such jumbo chips available, the challenge would still be toconvert all its generated lumens to the ±12-degrees needed in practicalimage projectors with high enough efficiency and spatial illuminationuniformity. At today's best LED lumen density of 50 lumens/mm², thetotal lumen yield from such a small illumination aperture would not benearly enough after projection system transmission losses to reachcompetitive projection screen powers, which must be at least 1000white-field lumens for many product applications of commercial interest.

[0005] The basic approach for overcoming this limitation has beendescribed previously and involves using spatially separated high lumendensity multi-layered arrays of separated red, green and blue LEDs,these arrays arranged and designed to concentrate their output emissionsto a particular range of narrowed output angles (and polarizationstates) that can be handled efficiently by the conventional optics of amodern image projection system. Once so-created and integrated with therespective reflective or transmissive LCDs (or reflective digitalmicro-mirror devices, DMDs or DLPs as trade marked by TexasInstruments), the LED array output beams are mixed using the standarddichroic mixing cubes that allow the single-colored beam apertures to besuperimposed on each other.

[0006] The present invention extends the basic approach to specific veryhigh lumen density illuminator embodiments that enable with the best ofthe forthcoming high-power flip-chip LEDs, a wide range of compact andpractical image projectors.

[0007] The present invention also extends to very low power, potentiallyhand held image projectors suitable for battery operation.

[0008] Such compact high lumen density LED illumination systems are alsoof interest for certain traffic signals and alerts, interior lighting,street lighting, stage and theatrical lighting, automotive head and taillighting, safety warning lights, the backlighting of LCD screens andcertain fiber optic medical illuminators.

[0009] These same compact high lumen density multi-layered illuminationsystems may be adapted for their intrinsic ability to display pixelizedimages directly, where in each reflecting bin within the light sourcearray involved contains one each of a red, green and blue LED, andwherein every LED in the array is individually-addressed.

SUMMARY OF THE INVENTION

[0010] It is, therefore, an object of the invention to provide animproved high lumen density illumination system and method of use.

[0011] It is another object of the invention to provide a multi-layeredpackaging means for a high lumen density light source panel structurecontaining a sparse two dimensional array of light emitting diode chipson a layer that provides discrete, thin-film electrical interconnectionsto the diodes, and that isolates one or more diode chips within separatespecularly reflecting compartments, the compartments themselves arrangedin a corresponding two-dimensional array that is covered with a stack ofoptical layers, one of which is a mechanical spacer including the binsthemselves that allows light transmission from each compartment to reachtwo light directing layers that include linear arrays of prism-likegrooves made in a clear plastic material, the grooves in each layeraligned at 90-degrees to one another.

[0012] It is a further object of the invention to provide a sufficientlyhigh lumen density light source panel system and method for providing anefficient and homogeneous beam of directional illumination to LCD andDMD spatial light modulators within compact video projection systems.

[0013] It is also an object of the invention to provide a multi-layeredpackaging means that combines a layer composed of an array ofmetallically reflecting bins having four tapered sidewalls, the bottomaperture of each bin containing one or more flip-chip LEDs protrudinginto the bin from an electrically interconnected back plane, theinterior of each bin either filled with air or a clear dielectricencapsulant, the bin apertures covered with a thin film stack consistingof two prism sheet layers and optionally a quarter wave phaseretardation layer and a reflective polarizing layer.

[0014] It is still another object of the invention to provide animproved system and a method for designing the geometry of the prismsheets operating in conjunction with the geometry of an underlyingLED-containing bin structure, such that output light concentrationwithin a selected angular range is increased maximized.

[0015] It is yet another object of the invention of provide an improvedsystem and method for fabricating relatively thin arrays of metallicallyreflecting bins made with an open lattice of input and output apertures.

[0016] It is further an object of the invention of provide an improvedsystem and method of designing thin arrays of metallically-reflectingbins whose geometry and sidewall shape is adjusted so as to maximize theangular and polarization state recycling brought about by reflectivemeans external to the bins themselves.

[0017] It is still an additional object of the invention to provide animproved system and method for constructing a hemispherical reflectorwithin a planar LED array based projector system such that thehemispherical reflector is formed on the inside wall of a cylindricalelement whose axis lies along the optical axis of the projection system.

[0018] It is yet one other object of the invention to provide animproved system and method for collecting and reusing light emitted by aplanar LED light source whose output angles miss the input aperture ofan angle transforming condensing lens such that the higher angle lightis instead intercepted by two sets of orthogonal and metallicallyreflecting sidewalls having ellipsoidal curvature, one focal line ofeach sidewall lying in the plane of the LED light source aperture, theother focal line of each sidewall lying on an input edge of asubstantially transparent light pipe positioned between the LED lightsource array and the condensing lens, the light pipe fitted with adistribution of light re-directing means that allow a portion of thecollected light to be directed out from the light pipe and into theinput aperture of the condensing lens.

[0019] It is additionally an object of the invention to provide animproved system and method for coupling planar multi-layered LED binarrays to LCD or DMD micro-displays by means of a secondary angletransforming or condensing element whose front and rear focal lengthsare matched to the approximate locations of the array's output apertureand the display's input aperture.

[0020] It is yet an additional object of the invention to provide animproved system and method for coupling a planar LED array light sourceto LCD or DMD micro-displays by means of a secondary angle transformingelement and an external hemispherical reflector positioned to collectand recycle all emitted light not collected by the transformingelement's aperture.

[0021] It is one further object of the invention to provide a compactmeans for efficiently recovering, re-circulating and reusing wide-angleoutput light from a multi-layered LED light source array by means of anexternally positioned reflector having either continuous or facetedspherical radius.

[0022] It is yet one further object of the invention to provide acompact means for efficiently recovering, re-circulating and reusingwide-angle output light from a multi-layered LED light source array bymeans of an externally positioned four-sided ellipsoidal reflector inconjunction with an elevated transparent light pipe having a partiallystructured surface plane

[0023] It is yet a further object of the invention to provide animproved system and method for forming the sloping sidewalls ofmetallically reflecting bin arrays such that the sidewall reflectionswhile non-scattering in nature, serve to randomize angular direction ofthe resulting light rays.

[0024] It is one other object of the invention to provide an improvedsystem and method for forming the LED and encapsulant surfaces withinand a part of metallically reflecting bin arrays such that theassociated reflections, while non-scattering in nature, serve torandomize angular direction of the reflected light rays.

[0025] It is a further object of the invention to provide an improvedsystem and method for efficiently transmitting light of one polarizationfrom an LED light source system through the input aperture of an LCDmicro-display device, while recycling and reusing light of theorthogonal polarization state by means of reflective polarizer andquarter-wave phase retardation planes, one associated with the inputaperture of an angle transforming element, the other the output apertureof a metallically reflecting LED light source array, combined with ahemispherical reflecting element, the focus of whose metallicallyreflecting interior is at or near the center-point of the LCD aperture.

[0026] It is one more object the invention to provide an improved systemand method for making a high efficiency multi-layered LED light sourcearray wherein one layer is a contiguous array of metallically reflectingfour-sided bins whose sidewall curvatures maximize the LED flux that isconveyed from input to output aperture in each X and Y meridian, whileparallel layers above this one are secondary light directing layersincluding two orthogonal cylindrical lenses or lens arrays whosecylinder axes are aligned in parallel with the bin array's orthogonalaperture diagonals, a quarter-wave phase retardation layer and awide-band reflective polarizer layer.

[0027] It is one more object the invention to provide an improved systemand method for making a silicon substrate containing a pattern ofelectrically conductive circuitry enabling the electrical bonding andinterconnection of one or two-dimensional arrays of physically separatedflip chip LEDs, arranged in rows and columns.

[0028] It is an additional object the invention to provide an improvedsystem and method for making one or two-dimensional arrays ofmetallically reflecting bins having sloped or tapered sidewalls whosearrangement allows physical through-holes in the array defining bothinput and output apertures, the associated input aperture arrayspatially arranged so that each input aperture matches the size andshape of each LED chip in a corresponding array so that when broughttogether each LED chip fits simultaneously through each correspondinginput aperture without mechanical interference blocking such a fit sothat each chip thereby protrudes into each bin.

[0029] It is also an additional object of the invention to provide acompact means for efficiently converting un-polarized output light froma multi-layered LED light source array into substantially polarizedoutput light using the metallically-reflecting nature of the reflectingbins involved and the metallically-reflecting nature of the LED'selectrodes, in conjunction with elevated polarization converting films.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1A illustrates in schematic cross-section a multi-layeredplanar LED light source array in which LED chips are contained in anarray of containers located beneath contiguous bins having plane taperedreflecting sidewalls whose bin apertures are beneath an upper and lowerprism sheet.

[0031]FIG. 1B illustrates in schematic cross-section a multi-layeredplanar LED light source array in which LED chips placed withincontiguous bins having plane tapered reflecting sidewalls whose binapertures are beneath an upper and lower prism sheet.

[0032]FIG. 2A illustrates in schematic cross-section a multi-layeredplanar LED light source array in which LEDs are placed in the aperturesof contiguous bins having curved reflecting sidewalls whose binapertures are beneath a polarization selective reflecting plane.

[0033]FIG. 2B illustrates a perspective view of a contiguous bin havingfour orthogonal mathematically shaped sidewalls.

[0034]FIG. 2C illustrates a perspective view of a contiguous bin havinga single mathematically shaped sidewall with optional vertical boundarywalls.

[0035]FIG. 3A illustrates in schematic cross-section a multi-layeredplanar LED light source array in which flip-chip LEDs are arranged in aregular array on a planar circuit plane, each LED protruding through theinput aperture of an array of contiguous bins having plane taperedreflecting sidewalls whose bin apertures are beneath a stack of filmscontaining a lower and upper prism sheet.

[0036]FIG. 3B provides greater detail of the schematic cross-section ofFIG. 3A specifically with regard to the insertion of a sub-mountedflip-chip LED into the secondary layer of contiguous micro-reflectingbins.

[0037]FIG. 4A contains a perspective view of an array of contiguousplane-walled reflecting bins, such as that represented in the schematiccross-section of FIGS. 3A-B.

[0038]FIG. 4B contains a perspective view of the tool structure used toform the array of reflecting bins illustrated in the perspective of FIG.4A.

[0039]FIG. 5A is a schematic cross-section of the front view of aone-bin region of the multi-layered LED light source array of FIGS.3A-B.

[0040]FIG. 5B is a schematic cross-section of the side view of a one-binregion of the multi-layered LED light source array of FIGS. 3A-B.

[0041]FIG. 5C is a perspective view of the two prism sheets as locatedabove the bin arrays illustrated for example in FIGS. 1A, 3A-B and 5A-C.

[0042]FIG. 6A is an illustrative exploded view of the basic flip chipLED structure as modeled herein, showing a substrate layer, an epitaxialcoating, the plane of rays immersed within the epitaxial material, andthe reflecting electrode structure.

[0043]FIG. 6B illustrates a top view of the reflecting electrode'sstriped structure.

[0044]FIG. 6C is an illustrative perspective view of the basic flip chipLED structure as modeled herein, showing, including in particular, itslocation and attachment to a mounting circuit.

[0045]FIG. 7 represents the graphical results in total effective outputlumens of a 40-bin LED light source array structured as in FIGS. 3 and 5as a function of bin depth and the type of films elevated above thebins.

[0046]FIG. 8 represents the graphical results in total effective outputlumens of a 40-bin LED light source array structured as in FIGS. 3 and 5as a function of the apex angle of prism sheets used and the bin depth.

[0047]FIG. 9 represents the graphical results in total effective lumensof an optimized 40-bin LED light source array structured as in FIGS. 3and 5 as a function of the apex angle of prism sheets used

[0048]FIG. 10 represents the graphical results in total effective lumensof a 40-bin LED light source array structured as in FIGS. 3A-B and 5A-Cas a function of both the apex angle of prism sheets used and bin depth.

[0049]FIG. 11 is a schematic cross-section illustrating the mechanism ofpolarization recovery and reuse in an LED light source array structuredas in FIGS. 3A-B and 5A-C showing the trajectories of illustrativeoptical rays as a function of their polarization.

[0050]FIG. 12 represents graphical results in total included lumens perbin for an LED light source array structured as in FIGS. 3A-B and 5A-C(curves A and B) contrasted with an array of bins, each of whichdesigned to preserve etendue (curves C and D).

[0051]FIG. 13 is a schematic cross-section illustrating the geometricalrelations in a projection system combining the LED light source array ofFIGS. 3A-B and 5A-C with a secondary angle transforming element and animaging device (either an LCD or DMD).

[0052]FIG. 14 represents graphical results in total effective lumens oftwo types of LED light source array structures, one havingstraight-walled bins and one having curved wall bins, both as a functionof prism sheet apex angle.

[0053]FIG. 15A is a schematic cross-section illustrating geometry andray paths for the optical system of FIG. 13 combined with ahemispherical light-recycling reflector.

[0054]FIG. 15B shows in a magnified cross-sectional view the type of LEDbin array as illustrated in FIGS. 3A-B that can be used in the system ofFIG. 15A without optical over layers.

[0055]FIG. 15C shows a single LED bin that can be used in the system ofFIG. 15A without optical over layers.

[0056]FIG. 15D shows the type of LED bin array illustrated in FIGS. 3A-Bthat can be used in the system of FIG. 15A with the addition of opticalover layers.

[0057]FIG. 15E shows a graphic illustration one type of commerciallyavailable LED package structure that can be used singly or in a tightarray within the system represented in FIG. 15A.

[0058]FIG. 16A shows a perspective view of the hemispherical reflectorsidewall as represented in FIG. 15A.

[0059]FIG. 16B shows a side view of the hemispherical reflector sidewallas represented in FIG. 15A.

[0060]FIG. 16C shows a top view of the hemispherical reflector sidewallas represented in FIG. 15A.

[0061]FIG. 16D shows a perspective side view of an alternativecylindrically segmented hemispherical reflector that can be used in thesystem represented in FIG. 15A.

[0062]FIG. 17 shows a schematic cross-section of the cylindricallysegmented hemispherical reflector shown in FIG. 16D as used in thesystem represented in FIG. 15A.

[0063]FIG. 18 is a schematic cross-section illustrating geometry and raypaths for the optical system of FIG. 13 combined with acorner-cube-based light-recycling reflector.

[0064]FIG. 19A is the schematic cross-section of a single taperedreflecting bin with constituent LED chip showing illustrative opticalray paths for LED emission and the behavior of incoming light rays.

[0065]FIG. 19B shows a magnified view of the tapered reflectingsidewall's surface flatness as represented in the schematic of FIG. 19A.

[0066]FIG. 20 is the schematic cross-section of a single taperedreflecting bin with constituent LED showing the geometrical effects ofrefraction by a single prism sheet elevated above, with illustrativeoptical ray paths shown both for LED emission and an incoming light ray.

[0067]FIG. 21A shows a magnified cross-sectional view of a triangularlyrippled surface boundary between the transparent dielectric fill and airwithin the output aperture of a micro-reflecting bin such as that shownin FIG. 20.

[0068]FIG. 21B shows another magnified cross-sectional view of arib-like rippled surface boundary between the transparent dielectricfill and air within the output aperture of a micro-reflecting bin suchas that shown in FIG. 20.

[0069]FIG. 21C shows yet another magnified cross-sectional view of acylindrically or spherically rippled surface boundary between thetransparent dielectric fill and air within the output aperture of amicro-reflecting bin such as that shown in FIG. 20.

[0070]FIG. 21D is the schematic cross-section of a single taperedreflecting bin with constituent LED chip showing illustrative opticalray paths for LED emission and an incoming light rays as affected by theexistence of rippled surface structures.

[0071]FIG. 21E is the magnified schematic cross-section of a singletapered reflecting bin with constituent LED chip in the vicinity of theLED showing illustrative optical ray paths for LED emission and anincoming light rays as affected by the existence of rippled surfacestructures of the LED's epitaxial layer, metallic reflecting electrodesand supporting substrate.

[0072]FIG. 22A is a schematic cross-section of an optical systemcombining the LED light source array of FIGS. 3A-B and 5A-C with asecondary angle transforming element, a structured light pipe plate anda four-sided elliptical reflector.

[0073]FIG. 22B is the associated perspective view of the schematiccross-section shown in FIG. 22A.

[0074]FIG. 23A is a more detailed schematic cross-section of the sideview of the optical system represented in FIG. 22A-B showing itsgeometric positioning within the optical system of FIG. 13.

[0075]FIG. 23B is a perspective view of on of the mathematically shapedreflecting sidewalls shown in FIG. 23A.

[0076]FIG. 24A is a perspective view of a slab-type structured lightpipe plate.

[0077]FIG. 24B is a perspective view of a light pipe plate with planebeveled end faces.

[0078]FIG. 24C is a perspective view of a light pipe plate withtruncated plane beveled end faces.

[0079]FIG. 25A is a schematic cross-section of the effects of light pipestructure on illustrative total internally reflecting light rays.

[0080]FIG. 25B is a magnified view of the lower light pipe surface asdepicted in FIG. 25A and the effect of a mesa-like surface structure onthe process of total internal reflection.

[0081]FIG. 25C is a perspective view of the mesa-like surface structuredepicted in FIG. 25B.

[0082]FIG. 26 is the schematic cross-section of a variation on theoptical system of FIGS. 1A-B3 that includes a hemispherical reflectorfor the recycling and reuse of polarized light.

[0083]FIG. 27 is a generalized schematic cross-section of the opticalsystems based on FIGS. 13, 15A-E, 17, 18, 22A-B, 23A-B, and 26incorporating planar LED light source arrays of FIGS. 3A-B and 5A-C.

[0084]FIG. 28A is another generalized schematic cross-section of theoptical systems based on FIGS. 13, 15A-E, 17, 18, 22A-B, 23A-B, and 26incorporating the planar LED light source arrays of FIGS. 3A-B and 5A-Cas well as other possible LED array structures.

[0085]FIG. 28B shows a magnified cross-sectional view of themicro-reflecting LED bin array type of FIG. 3A as one possible choicefor use in the optical system of FIG. 28A without optical over-layers.

[0086]FIG. 28C shows the magnified view of a single LED bin that can beused in the system of FIG. 28A without optical over layers.

[0087]FIG. 28D shows the type of LED bin array illustrated in FIG. 3Bthat can be used in the system of FIG. 28A with the addition of opticalover layers.

[0088]FIG. 28E shows a graphic illustration one type of commerciallyavailable LED package structure that can be used singly or in a tightarray within the system represented in FIG. 28A.

[0089]FIG. 29A is the schematic side view cross-section of amulti-layered planar LED light source array in which flip-chip LEDs arearranged in a regular array on a planar circuit plane, each LEDprotruding through the input aperture of an array of contiguous binshaving curved reflecting sidewalls designed so as to preserve etenduefrom input to output aperture and whose bin apertures are locatedbeneath an elevated stack of polarization converting films.

[0090]FIG. 29B is a perspective view of the multi-layered planar LEDlight source array depicted in FIG. 30A.

[0091]FIG. 30A shows the Lambertian angular output distribution of anLED light source, such as the micro-reflecting array depicted in FIG.30B.

[0092]FIG. 30B is a schematic cross-section of an LED array of truncatedetendue-preserving micro-reflecting bins whose centers have been pushedcloser together than physically possible, with the reflector truncationline placed at the onset of reflector overlap.

[0093]FIG. 31A shows the non-Lambertian angular output distribution ofan LED light source such as that of FIG. 31B whose behavior has beenmodified so as to increase light emission at lower angles at the expenseof light emission at higher angles.

[0094]FIG. 31B is the schematic cross-section of the truncated LED arrayshown in FIG. 30B with the addition of two prism sheets elevated abovethe array to replace the overlapping reflector region that had beenremoved as the result of the truncation.

[0095]FIG. 32A shows the schematic top view of a 3×3 LED light sourcearray composed of the contiguous etendue-preserving reflector bins asillustrated in FIGS. 29A-B with light output (˜93 lumens) as representedfor the case when only the center LED has been lighted.

[0096]FIG. 32B shows the schematic top view of a 3×3 LED light sourcearray composed of the contiguous etendue-preserving reflector bins asillustrated in FIGS. 29A-B with light output shown for the case when all9 LEDs have been lighted.

[0097]FIG. 33A shows the top view of a 3×3 LED light source arraycomposed of the contiguous non-etendue-preserving reflector bins andelevated prism sheets shown in FIGS. 3A-B and 5A-C and depicts the 9-binarray's light output for the case when only the center LED has beenlighted.

[0098]FIG. 33B is a perspective view of the 3×3 LED light source arrayof FIG. 33A.

[0099]FIG. 34 shows the graphical result of the fraction of totaleffective lumens produced by the single lighted bin of the LED lightsource array of FIGS. 33A-B as a function of the size of the outputsquare area considered, for light within two similar angular ranges(±25-degrees, triangles Δ; ±30-degrees, squares, □).

[0100]FIG. 35A is a schematic representation of one type of sub-mountedflip-chip LED having a hexagonal sub-mount circuit with positive andnegative contacts on opposing hexagonal points.

[0101]FIG. 35B is a schematic representation of one type of sub-mountedflip-chip LED with square sub-mount circuit.

[0102]FIG. 35C is a schematic representation of another type ofsub-mounted flip-chip LED having a hexagonal sub-mount circuit withpositive and negative contacts on opposing hexagonal edges.

[0103]FIG. 35D is a schematic back-side representation of anillustrative series-parallel electrical interconnection circuit appliedto the bottom of the metallically reflecting bin arrays shown in thecross-sections of FIGS. 3A-5C and 29A-B, the bin arrays used as a meansof attaching and interconnecting an array of the discretely sub-mountedflip-chip type LEDs shown in FIGS. 35A-C.

[0104]FIG. 35E illustrates by means of a cross-sectional view how asub-mounted LED of FIGS. 35A-C is assembled to the micro-reflecting binarray depicted in FIG. 35D.

[0105]FIG. 36 is a schematic representation of the micro-reflecting binarray of FIG. 35D except for the use of a different series-parallelelectrical interconnection circuit.

[0106]FIG. 37 is the schematic representation of another illustrativeseries-parallel electrical interconnection circuit applied to the topsurface of a planar substrate for the purpose of attaching andinterconnecting an array of un-mounted flip-chip LEDs for use with thebin arrays of FIGS. 3A-5C and 29A-B.

[0107]FIG. 38 is the schematic representation of the completely parallelelectrical interconnection circuit applied to the top surface of aplanar substrate circuit for the purpose of attaching andinterconnecting an array of un-mounted flip-chip LEDs for use with thebin arrays of FIGS. 3A-5C and 29A-B.

[0108]FIG. 39 shows graphical results for the lumens produced by asingle 1.6 mm bin in the optimized LED light source array of FIGS. 3A-Band 5A-C as a function of the enclosed angular range of emitted outputfor three LED bin array cases: no elevated prism sheets, elevated prismsheets with 90-degree prisms and elevated prism sheets with optimized104-degree prisms.

[0109]FIG. 40 is a schematic representation of the top view of an 8×8bin LED light source array with all 64 LEDs operating, showing thespatial output percentage contributed by each 1.6 mm square bin region.

[0110]FIG. 41A is a schematic representation of the top view of thecentral 6×6 bin portion of the 8×8 bin LED light source array of FIG.40, showing the total lumens contributed by each 1.6 mm square binregion when one binned LED in the array emits half as many lumens as allothers.

[0111]FIG. 41B is a schematic representation of the top view of anillustrative 3×3 bin array portion of the 6×6 bin array depicted in FIG.41B, showing the detailed lumen contributions from neighboring bins inthe array.

[0112]FIG. 42A is a schematic representation of the etendue-preservingbins of FIGS. 29A-B supplemented by two elevated cylindrical lenseswhose cylinder axes are aligned with bin-aperture diagonals to improvediagonal-meridian field coverage.

[0113]FIG. 42B is a schematic representation of the etendue-preservingbins of FIGS. 29A-B supplemented by two elevated lenticular lens arrayswhose cylinder axes are aligned with bin-aperture diagonals to improvediagonal-meridian field coverage.

[0114]FIG. 43 is a schematic cross-section of an illustrative videoprojection system for three reflective LCDs, based on the focal planeoptical system layout of FIGS. 1A-B3 and the planar light source arraysof FIGS. 3A-B, 5A-C, 11, 29A-B and 42A-B.

[0115]FIG. 44 shows graphical results for the white lumen screen outputof the projection system of FIG. 43 using the non-etendue-preserving LEDlight source arrays of FIGS. 3A-B, 5A-C and 11 as a function of both thecondensing element's effective focal length in air and the total numberof 1.6 mm bins in each (red, green and blue) array.

[0116]FIG. 45 is a schematic cross-section of an illustrative videoprojection system for three transmissive LCDs based on the focal planeoptical system layout of FIG. 13 including the planar light sourcearrays of FIGS. 1A-3B, 5A-C, 11, 29A-B and 42A-B (shown illustrativelywith the etendue-preserving light source array of FIGS. 42A-B).

[0117]FIG. 46 is a schematic cross-section of an illustrative videoprojection system for a single transmissive LCD operatedfield-sequentially based on the focal plane optical system layout ofFIG. 13 and the planar light source arrays of FIGS. 1A-3B, 5A-C, 11,29A-B and 42A-B (shown illustratively with the etendue-preserving lightsource array of FIG. 42A-B).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0118] The present inventions relate to multi-layered packagingstructures whose structural details maximize optical output from arraysof interconnected light emitting diodes (LEDs) over earliermulti-layered packaging structures. Specifically, the present inventionsallow for the highest possible concentrations of output lumens persquare millimeter of output aperture. This improvement leads to designsthat allow earliest possible use of LED arrays as practical replacementsfor light bulbs in demanding applications such as video projection. Thisimprovement also leads to related designs that use the minimum number ofLEDs for the intended purpose.

[0119] Previous inventions, such as 10 in FIGS. 1A-B and 66 in FIG. 2A,have described the use of specially-shaped and sized reflecting binssurrounding each LED (or groups of LEDs) in the array with the binsarranged to work in conjunction with the design of certain reflectivemulti-layers placed just above them, such as for example prism sheets 4and 6 in FIGS. 1A-B and reflective polarizer 56 in FIG. 2A. The shape ofthe reflecting sidewalls 2 (and in 22) in FIGS. 1A-B and 50 in FIG. 2Ais adjusted to redirect output light towards the reflective multi-layersfrom LED 20 in FIGS. 1A-B (or the enclosed LED emitter 70 in FIG. 2A).Multiple reflections between reflective elements are then employed totransform the output angular distribution of light passing through thesystems 10 and 66 in a favorable way for a variety of lightingapplications. While this multi-layered approach provides a basis forachieving high-density output light from arrays of LEDs, no workingrelationship has yet been established for maximizing the array's outputdensity.

[0120] The form introduced in FIGS. 1A-B and shown with flip-chip LEDs20 uses shallow reflecting bins 12 with plane, tapered sidewalls 2. LEDlight enters bins 12 through aperture 24 from sub-bins 22 that containthe flip-chip LED (or LEDs) 20 and encapsulant 14, located just beneaththe main bins. Flip-chip LEDs consist of transparent substrate layer 42and epitaxial device layers 40 within which a diode is formed and lightis generated. Electrical contacts (combined with highly-reflectiveunder-surface mirror) 44 allow attachment to sub-mounts 24 and heatextraction layers. The sub-bins 22 surrounding the LED chips, also withshaped reflecting sidewalls 16, collect and convey LED light emittedthrough its substrate 42 and then through bin aperture 24 (and optionaldiffusing layer 8). One particular configuration is shown in FIGS. 1A-Bin which the sub-bins 22 and main bins 12 are formed as a continuousentity, sharing common dielectric medium 18, and having the samesidewall slope 38 (angle α measured from the vertical).

[0121] The form of FIGS. 1A-B operates with its two prism sheets 4 and 6elevated above the LEDs preferred heights G1′ and G1′+G4 so that lightreflected from the bins is controlled in both angle and spatialdistribution. Additional reflective polarizer layers 28 are added whennecessary to control output polarization as well. When the prisms aremade to have 90-degree apex angles, output preference 36 is given toangles within ±22.5 degrees. Beam uniformity depends on the factors ofprism sheet spacing.

[0122] The analogous form of FIGS. 2A-C is one that replaces the role ofthe reflective angle-controlling prism sheets by the curved shape of thebin sidewalls 50. By doing so, output light from the bins is even moretightly controlled in angle, and polarization, by reflectiveinteractions with polarizer layer 56 elevated above the bins.

[0123] While both structural forms of FIGS. 1A-B and FIGS. 2A-C yieldangularly-directed output beams from seamlessly arranged outputapertures, neither system's optical efficiency (expressed in outputlumens falling within a specified angular range divided total LED lumensemitted) and output density (output lumens falling within a specifiedangular range divided by the aperture area) has been maximized.

[0124] The importance of maximizing LED array output can be illustratedby the difficult performance requirements presented by a modern LCD orDMD (DLP) video projector needing to deliver over 1000 white-fieldlumens to the (front or rear) projection screen. One common RGBwhite-field distribution is 60% green, 30% red and 10% blue, requires600 green screen lumens, 300 red screen lumens, and 100 blue screenlumens. Suppose the projector uses three reflective LCDs at f/2.4, onefor each color, each of whose aspect ratios are 4:3 and each of whosediagonal size is 1.2″. Taking the green channel as the critical example,with a 90% efficient projection lens and an 81% transmissive dichroiccolor-splitting cube, one finds that there must be 823.7 polarized greenlumens at the reflective LCD within an angular range of ±12-degrees(i.e. f/2.4). Then using the pseudo-Kohler polarizing beam-splitter typeangle-transformer (25-degree to 12-degree) we've described previously,and that is explained later in more detail, one finds that theassociated LED array illuminator must be capable of supplying 1170polarized green lumens within ±25-degrees. Any light generated in anglesgreater than ±25-degrees cannot be viewed. Moreover, the 1170 lumen beammust be produced within a specific rectangular aperture area defined byfundamental geometric expressions related to the LCD's spatial andangular aperture. (Note: Square apertures may also be used, and thisvariation will be discussed further below.) Specifically, and from thewell-known Sine Relation, the illumination aperture edges, X_(ILL) andY_(ILL), are as in equations 1 and 2.

X _(ILL) =X _(LCD) Sin(12)/Sin(25)   (1)

Y _(ILL) =Y _(LCD) Sin(12)/Sin(25)   (2)

[0125] Accordingly, with X_(LCD) and Y_(LCD) being 24.384 mm and 18.288mm respectively, the LED illuminator aperture becomes approximately 12mm by 9 mm (there is a more detailed discussion further below). Anylight created outside this aperture area cannot fall usefully within theLCD aperture. So, for a sufficient number of green lumens to reach thescreen, it must be practical to produce 1170 polarized green lumenswithin this particular 108-mm² illumination-aperture area; those lumensconfined to ±25-degrees.

[0126] Doing so represents a significant challenge without deploying anarray of LED chips within a suitably efficient high-densityangle-controlling package.

[0127] As one indication of this difficulty, consider that the latest5-watt high-power LED package manufactured by LumiLeds (as Luxeon™)emits 120 un-polarized green lumens over a ±90-degree Lambertian angulardistribution from a domed circular lens (shown later) that isapproximately 4 mm in diameter. Assuming for the moment that such 4 mmdomes can be closed-packed (and they can't because of their externalpackage and electrode design), it can be shown from geometry that theluminous effect of only a total of 7.5 lens domes can be accommodatedwithin the illustrative 9 mm×12 mm illumination rectangle. These 7.5domes produce 900 un-polarized lumens within ±90-degree rather than the±25-degrees needed. LumiLeds reports in published data sheets that halfthis luminous power (450 lumens) exists within ±60-degrees, whichimplies that only 107 un-polarized lumens exist within ±25-degrees. Evenallowing for 100% polarization conversion efficiency (about 50% ispractical), such an array falls short of the projector need by more thana factor of ten.

[0128] The LED chips used by LumiLeds within this Luxeon™ package are 2mm by 2 mm squares. Assuming the package is nearly 100% efficient inrouting lumens generated by this chip into usable output, the 5-wattchip would be emitting at a density of 30 lumens/mm². If electricalefficiency were no object (and it is), as many as 27 such super-chipscould fit into the required 12 mm by 9 mm illumination aperture,yielding 3,240 un-polarized lumens over ±90-degrees, or 1,620un-polarized lumens over ±60-degrees. The yield within ±25-degrees wouldtherefore be 385.8 un-polarized lumens, and with 50% conversionefficiency, 289.3 polarized lumens. Even such a monster array running at135 watts falls short of the projector's green lumen need by a factor offour.

[0129] It has been established that the emitting density of these samehigh-power flip-chip LEDs is currently as high as 50 lumens/mm², andthat by 2004, with twice the power density (or less) able to betolerated, will rise to the 100 lumens/mm² level. Despite such advances,the monster array just described would generate 6,480 un-polarized greenlumens over ±90-degrees at 270-watts. This would produce 1157 polarizedgreen lumens, which is just about the number needed. Yet, the wattagenecessary for this is impractical, as total projector power for R-G-Bwould rise above 550 watts.

[0130] What is needed, even with the highest-performing LEDs, is a moreangularly efficient LED illumination array than would exist by suchconventional means.

[0131] The present inventions, shown in three basic forms, addressingthis and related needs, are based on the two original forms shown inFIGS. 1A-B and in FIGS. 2B-C. Each better facilitates such practicalhigh-lumen density applications, particularly video projection, where asit has been seen, very high numbers of lumens are required within anarrow angular range and a confined spatial area. The improved formsalso facilitate practical applications in other areas, such as trafficsignaling, where commercial priorities seek the costs reductionspossible when using the fewest number of LEDs possible.

[0132] A. First Form: Shallow-Profile Multi-Layer LED Arrays UsingStraight-Walled Bins and Modified Prism Sheets (as in FIGS. 3A-B and5A-C)

[0133] The first form of the present invention is shown in FIGS. 3A-B,and involves the use of a continuous and regular array structurecomposed of shallow reflecting bins 82 with plane sidewalls 106 locatedjust beneath a vertical stack of reflecting films covering the binapertures that includes two orthogonally-oriented prism sheets 88 and 92with modifications, and optionally, a quarter-wave phase retardationfilm 86 and a reflective polarizer 84. This compact form, an extensionof the previous form shown in FIGS. 1A-B, achieves highest possiblelumen density by permitting the densest allowable array of LED chips 118on the systems 90 back plane 94. Rather than placing LED chips in arrayshaving empty spaces 105 between the LEDs that equal the size of the LEDsthemselves, this structure allows a tighter packing of LEDs, limited bythe bin's sidewall angle α, 38, which depends on its constructiverelationship with the design of the prism sheet layers 88 and 92.

[0134] Moreover, the spacing between the LED array and the modifiedprism sheets is set by the depth of the shallow reflecting bins 82, andnot by a gap between the lowest prism sheet and the bin layer itself. Assuch, optimum performance depends on the geometric relationship existingbetween the bin and prism structures.

[0135] The LEDs used in this structure may be of any form or number, butare best made in the so-called flip-chip style 118, wherein atransparent substrate material 120 (currently sapphire) is combined withepitaxial layers 122 (currently gallium nitride based) whose structureand adjacent electrodes 114 and 116 act to form the p-n junctions thatgenerate emitted light. Electrodes 114 and 116 have been madereflecting, so that any emitted light directed towards these elementsreflects towards the transparent substrate layer, and thereby, outwardsfrom the LED.

[0136] One particular advantage of orienting the LED chip with itselectrodes facing downwards is that it reduces the difficulty of makingelectrical interconnection. In this case, a process known assolder-bumping is best used to re-flow solder material deposited betweenthe LED electrodes and counter-positioned bars (or stripes) 100 and 108placed on the mounting surface (either a back plane 94, or as shown inthe example of FIGS. 3A-B, a sub-mount 112. Another advantage of theflip-chip orientation is that it provides lowest possible thermalresistance from the source of heat-generation (the electrodes and p-njunction) and the heat extraction layer 96 attached to LED-mounting backplane 94. It is crucial to minimize all thermal resistance paths, as thesystem's net thermal resistance determines its steady-state temperatureduring operation, which must be limited to values less than about 150 Cor risk significant performance degradations from material failures.

[0137] The cross-sections shown in FIGS. 3A-B represent only a singleLED chip within each bin unit. While modern LEDs can be operateddirectly in air, best performance is achieved when encapsulated in ashigh a refractive index medium as feasible (typically around 1.49) 101.The reason for this dielectric encapsulation 101 is to minimize theamount of light emission in the light generation layer 122 that can beretained within this layer and within the attached device substrate 120by total internal reflection. It is well known that the critical anglefor total internal reflection depends on the difference of refractiveindex between the light containing medium and its surroundings. Thebigger this difference, the more luminous energy is trapped by totalinternal reflection, and thereby lost to application.

[0138] The geometric form of the bin structure of FIGS. 3A-B is aspecial case of the bin structure described in our previous inventionswith sub-bin layer 22 and main bin layer 12 made so as to have the samesidewall angle α, 38, and the same internal dielectric medium 18, as inthe lower part of FIGS. 1A-B. This bin structure 126 is fabricated, asshown schematically in FIGS. 4A-B, using tooling 128, formed to thenegative (or reverse) shape of the array structure 126 to be formed. Forthe symmetrical (square) bins shown, the form tool 128 can be made as inFIG. 4B from a base metal substrate, for example, by plunge cuttingrepetitively ruled lines using a specially shaped diamond tool, shapedso that the final total included groove angle is 2α, α being thesidewall angle 38 as shown in FIGS. 3A-B. Other equally well establishedcutting methods such as single-point or fly cutting may be used as well.Once a properly shaped form tool is created, it is used as the masterfor any one of a number of well-established forming processes such aselectroforming, molding, embossing, and cast-and cure that result in theformed part 126 as shown in FIG. 4A. Form tool mesas 135 may be slightlyextended so as to be able to punch through casting, molding or embossingproducts to assure clean and clear through holes are made in resultingpart 126.

[0139] Guidelines 130 in FIG. 4 show how a portion of formed part 126 inFIG. 4A removes from a portion of the grooved pattern in form tool 128in FIG. 4B. It is equally feasible to form bin part 126 by anyappropriate direct forming methods such as for example, chemicaletching, electro-discharge machining, and depending on the actual binsize, wire electro-discharge machining. Of these, an advantage offorming the bins of a conductive material such as metal, is that themetal adds to the heat extraction capacity of the system, diffusing heatthroughout the structure and away towards its underlying heat extractionlayer 96 (FIGS. 3A-B). Whether bin part 126 is formed in metal orplastic, its sidewall surfaces are subsequently (or contemporaneously)coated with a high reflectivity, specularly reflecting film such asprotected silver or enhanced aluminum.

[0140] In cases where the flip-chip LEDs 118 are pre-mounted by theirmanufacturer on individual sub-mounts, 112 in FIGS. 3A-B, the undersideof the bin part is used conveniently, as described later on, as thesubstrate for associated electrical interconnection stripes 100 and 108.

[0141] The bin part 126 may also be an artifice for mechanicallysupporting a dielectric encapsulating bin structure 101 that ordinarilyfills in within the internal cavities of a physical structure such as126. In this case, the reflecting sidewall becomes the internalsidewalls of the dielectric structure bounded not by metal, but by thethin layer of air between uncoupled dielectric and metal surfaces. Thephysical shape of this dielectric structure directly mimics the physicalshape of form tool 128, with the principal difference being that it ismade instead of an uncoated optically clear and transparent dielectricmaterial. A traditional advantage for reflecting light from such adielectric air boundary, rather than a dielectric metal boundary is thatthe reflectivity achieved in making a total internal reflection (TIR)can be considerably higher than that of a purely metallic reflection.Counterbalancing gains made by the improved reflectivity of a dielectricreflecting structure, however, are the losses of light rays that failTIR and escape the dielectric into air. These losses, if not averted,could create a preference for using metallic reflecting walls 106 thathandle all rays. One way to avert such losses is to combine use of areflecting bin structure (shaped as 126 in FIG. 4A) with a dielectricinsert (shaped as 128 in FIG. 4B). When this is done, all light coupledinto the dielectric from the LED chip makes it through the bin's outputaperture X_(i), 98, through the dielectric 101, either directly, or byexternal reflection across the air-gap from the decoupled metalreflecting surface. The only drawback to taking this approach is thatthe LED chip must be immersed within dielectric medium 101. This isstraightforward when filling physical bins 126 (FIG. 4A) with acompliant dielectric material such as a silicone, but less so wheninvading the LED-chip into a preformed dielectric material. One methodfor accommodating this approach would be to pre-form a smallchip-sized-boss in the forming tool, so that it would create achip-sized well in the formed dielectric. An optical adhesive would thenbe used to make optical contact between chip and dielectric.

[0142] The primary improvement in the present invention, aside from itsmore realistic flip-chip LED mounting structure, and its shallow binstructure, is in the construction and location of the two elevated prismsheets 88 and 92, shown in more detail in FIGS. 5A-C.

[0143] B. Bin Depth and Modified Prism Sheets

[0144] In the new invention, bin depth G1, 102, as in FIGS. 5A-B is usedto set the best gap between prism sheets 88 and 92 (also shownseparately in FIG. 5C), and the emitting plane of the LED array. In theprevious invention, the gap between the lower prism sheet and the LEDarray was set not only by bin depth, but also by a physical spacingbetween the prism sheet substrate and the top of the bin layer.

[0145] It will be shown that arbitrary bin depth may significantlyrestrict the array's effective output lumens.

[0146] The prism sheets themselves may also be modified as in FIGS.5A-C, not only so that their apex angle β₁+β₂ (138 and 140) optimizereflective interaction with underlying shallow bin layer 82, but sothat, in certain cases, substrate layers 161 may be altered, forexample, with a positive or negative cylindrical lenticular lensstructure. The inclusion of such optional diffusing structures iswarranted when their beneficial effect on overall beam uniformity isdesired.

[0147] In the original invention, the two orthogonally oriented prismsheets (see 4 and 6 in FIGS. 1A-B) use parallel 90-degree prismaticgrooves on otherwise planar substrates, similar to 3M's commerciallybrightness enhancement film (BEF™). 3M's 90-degree BEF prism sheets areused to increase viewable brightness in flat panel LCD screens (such asthose used in laptop computers and desktop monitors). Unlike BEF, whichis typically placed directly against a passive flat panel backlight andjust behind the LCD screen to be illuminated, the present prism sheetsare each elevated specific distances with respect to the source of light(i.e. the binned LED array) and to each other, as in FIGS. 1A-B. Sheetelevation is used to achieve a best position for the four virtual imagesof each LED's emitting region created by the sheets, with the goal ofimproving overall spatial uniformity of the illuminating beam generatedby the LED array across the output aperture.

[0148] When the goal is also to maximize the total number of outputlumens in a beam of light coupled from the reflectively-binned LED arraywithin a given angular range (say the ±25-degrees needed by the videoprojector example above), the conventional prism sheet (using planesubstrates and prism grooves whose apex angle is 90-degrees),arbitrarily positioned above the source of light, does not produce thebest possible performance.

[0149] The preferred structure is shown in FIGS. 5A-C in terms of itsfront (FIG. 5A) and side view (FIG. 5B) cross-sections, and aperspective view (FIG. 5C) of the two modified prism sheets. In thepreferred configuration, bin layer 82 has depth G1, 102, and a sidewallangle measured from the vertical, γ, 39, the relationship between them,as in equation 3, governed by the size X_(c) 97, of LED chip 118, therelative size of the bin bottom, X_(i) 100 and the bin's output apertureX_(o), 98, in each meridian (front and side views). While optimum valuesdepend on the specific nature of reflective interactions between the bingeometry and the geometry of the modified prism sheet superstructure itis the size of the bin's output aperture, X_(o), which first establishesthe density (and number) of LEDs within the array. The larger ratio ofoutput to input aperture (X_(o)/X_(i)), the sparser the array; and thesmaller the ratio of output to input aperture, the denser the array.

Meridian (X or Y): G 1=(X _(o) −X _(i))/2 Tan γ  (3)

[0150] There are practical limits to the density with which today's LEDscan be arranged in 1D and 2D arrays, primary driven by cost and totalsupportable wattage. The higher the LED wattage required per squaremillimeter, the more difficult is the task of heat extraction, as willbe discussed in more detail later.

[0151] The modified prism sheets consist of prism apex angles that arethe sum of the angles β₁, 138 and β₂, 140, and a substrate layeroptionally containing positive or negative cylindrical lenticular lensstructures, radius of curvature, R. In each sheet where they arecontained, the cylindrical lens axes run substantially parallel to theaxes of the corresponding prism grooves. Prism sheet diagonals (141 inlower sheet 92 and 143 in upper sheet 88 as in FIG. 5C) are preferablyaligned orthogonally to one another, but may be aligned in any angularorientation to bin aperture diagonals 129 and 131 as in FIG. 4A.

[0152] C. Method of Optimization

[0153] A fully parameterized and predictive computer model isconstructed to explore the underlying effect on performance between binarray and prism sheet geometries. The advantages of using a predictivemodel for this purpose rather than more traditional laboratoryexperiments are flexibility, time-efficiency, and cost. Fabricating adiverse enough combination of bin array and micro-prism sheet geometrieswould be a sizable and costly challenge. Even if cost were no object,there would be practical limits on the degrees of fineness over whichthe geometric variables could be explored.

[0154] Aside from the geometric relations of equation 3, no equivalentlysimple mathematical relationships can be derived between the parametersof equation 3 and the prism sheet parameters, β₁ and β₂ for the lowersheet, R for the lower sheet, β₁ and β₂ for the upper sheet, R for theupper sheet, G2 and G4. While the mechanisms of reflection andtransmission at each interface are well understood, and based only onthe laws of reflection and refraction at metallic and dielectricinterfaces, mathematical complexity arises from the need to quantify thecollective behavior of a large number of geometric light rays, travelingboth in and out of the plane of FIGS. 5A-C (i.e., paraxial and skewrays). This need is traditionally addressed by means of a ray-tracingprogram that follows the paths of a large number of randomly generatedrays from their point of origin to their point of destination.

[0155] Such approach was taken for the system 90 of FIGS. 3A-B, subjectto cross-sectional details provided in FIGS. 5A-B. The operative laws ofray trajectories in complex optical systems, especially those with onlyreflective, refractive and absorptive processes, are confidently andreliably represented by almost any of the commercial ray-tracingsoftware products made for this purpose. Present work was performedusing ASAP™ 7.0, a product of Breault Research Organization, Tucson,Ariz. in a straightforward manner.

[0156] Computing accuracy depends chiefly on the realism with which thesource of rays is represented, the source in this case needing to be amodern flip-chip LED. That said, the system 90 of FIGS. 3A-B is actuallya non-imaging optical system, and because of this, does not benefit frommore detailed representations of the exact device physics within theLEDs themselves than is necessary. All that is needed is a reasonablegeometric approximation of the flip-chip type LED used to givesufficient optical representation of the LEDs most critical structuralmechanisms.

[0157] A detailed description of the flip-chip LED source model we usedis provided in FIGS. 6A-C, after the generalized flip-chip cross-sectionsymbolized in FIGS. 3A-B. This model is meant to be a reasonablerepresentation of the high power green and blue galliumnitride-on-sapphire LEDs currently manufactured by LumiLeds. TheLumiLeds LEDs feature a novel (and highly-reflective) inter-digitatedelectrode structure 125 (125A and 125B), represented in FIG. 6B thatserves as a mirror. No attempt was made to faithfully approximate thestructure of this mirror, as it covers practically the entire deviceaperture. The gallium nitride epitaxial layers 122 (refractive indexabout 2.4) are split as 122A and 122B to indicate the approximatelocation of the emitting plane 123 where rays are generated randomlyspatially within the plane and over every possible angular direction.The sapphire substrate (refractive index about 1.8) is about 100 micronsin thickness. Many rays generated within epitaxial layers 122 remaintrapped within this high refractive index wave-guide. Rays that escapethe epitaxial layers do either through their bounding edges or throughthe interface with sapphire substrate 120. Similarly, rays that escapetotal internal reflection within the sapphire substrate, escape asoutput through the 5 exposed sapphire faces.

[0158] As in FIGS. 3A-B and 5A-C, the refractive index surrounding(encapsulating) flip-chip LED 118 is typically about 1.49. The sourcemodel is pre-calibrated against reported (or expected) experimentalresults for the bare device. Calibration variables include the thicknessin microns of the epitaxial layer 122 (taken as being about 2 microns),the reflectivity of electrode mirror 125 (taken as being about 0.89) andthe average lumens/mm² that are actually created within the device'ssimulated p-n junction plane 123. Calibration consists of collecting andanalyzing all output rays in total lumens, and comparing this resultwith the experimentally observed result. Until the model value and theexperimental value agree, judicious changes are made to any of theperformance controlling variables. In this particular case, it is lessimportant that the variables actually represent their physical realitythan that they combine to allow correct simulation of the LEDs totaloutput lumens.

[0159] Once the LED source is reliably calibrated, it is incorporatedwithin the complete illumination system 90 of FIGS. 3A-B with confidencethat the system's output predictions are found to be just as accurateand realistic.

[0160] D. Geometrical Relationships and Their Effect on LED IlluminatorPerformance

[0161] The total number of output lumens contained within a requiredangular range specifies LED illuminator performance.

[0162] As one example of illumination system 90 of FIGS. 3A-B we use theLED source model described above, and the case of an array of 1 mmsquare LumiLeds type flip-chip LEDs, 118, capable of generating 100lumens/mm² (the performance expected of the best quality LumiLedsproduction units by the first half of 2005).

[0163] The array's aperture, consistent with the projector example givenabove, is limited approximately to 12 mm×9 mm rectangular (or 12 mm×12mm square) cross-sections, and effective illumination angles ofnominally ±25-degrees. The number of LEDs used in this array is limitedto about 40-50 chips, to control cost and wattage. This means for thecase of square bin apertures, that X_(o) is 1.6 mm (i.e.,(12)(9)/(1.6²)=42 or (122)/(1.62)=56). Allowing a small margin at thebottom of the bin around the LED chip, X_(i) becomes 1.1 mm, and thebin's sidewall angle, a, a geometric function of bin depth G1, 102 (inFIGS. 3A-B) governed by equation 3.

[0164] Other configuration variables are shown more clearly in FIGS.5A-B, and include lower prism sheet gap spacing G2, 132, lower prismsheet lens radius R_(L), 144, lower prism sheet apex angle β₁+β₂, upperprism sheet gap spacing (relative to the top of the lower sheet) G4, 31,upper prism sheet lens radius R_(H), 142, and lower prism sheet apexangle β₁+β₂. For simplicity the quarter-wave layer 86 and the reflectivepolarizer layer 84 are not included in the analysis.

[0165] There are some cases where including a lens structure 142 or 144on the prism sheets substrate layers 161 improves the number ofeffective output lumens, spatial beam uniformity, or both.

[0166] All output rays are collected on a large absorbing plane placeddirectly above the apex points of upper prism sheet 88. The total fluxover all angles (±90-degrees) reflects the overall collection andtransmission efficiency of system 90. The flux fraction found within anangular range of ±25-degrees is a critical measure of merit for thevideo projector application example, and the performance indicator to bemaximized, as will be developed in greater detail below.

[0167] Best results for the 1 mm LED chips in the 1.6 mm bins describedare achieved with 174-micron bin depth and symmetric 52-degree prismapex angles, α.

[0168] The development of this unique design combination results fromthe following analysis.

[0169] E. Effect of Bin Depth and Prism Angle

[0170] The best performing LED array illuminator produces the highestnumber of output lumens within the angular range required to achievefull (LCD or DMD) field coverage (in this case ±25-degrees), and does souniformly over the LED array aperture. This behavior depends on acooperative relationship between reflective bin depth 102, GI, and thefull apex angle, β₁+β₂, of the prisms in prism sheets 88 and 92, as inFIGS. 5A-B.

[0171] The importance of bin depth 102 in effecting maximum possibleoutput performance is traced for three particular straight- orflat-walled cases in FIG. 7: bins only (curve 141), bins and sheets ofcommercial brightness enhancement film BEF (curve 143), and bins andcrossed sheets of specially-optimized prismatic lumen enhancement filmLEF (curve 145).

[0172] For the case of binned flip-chip LEDs by themselves, there is aslight output peak of about 1000 lumens for the array at a bin depth of135 microns, which is just slightly deeper than the chip thicknessitself (see curve 141 in FIG. 7). As will be discussed later, the bindepth corresponding to this peak performance closely approximates thebehavior of ideally shaped curved-wall non-imaging optical concentratorbins.

[0173] When two commercial prism sheets are added directly above thebinned LEDs, each with 90-degree apex angles and prism grooves runningperpendicularly with each other, the output peak rises 28% to about 1280lumens, with the associated bin depth increasing to about 174 microns(see curve 143 in FIG. 7). This result emphasizes the importance of bindepth as a critical design factor. There is little or no performancegain seen when the prism sheets are used above 135-micron deep bins;yet, when the same prism sheets are used above 174-micron bins, theapparent gain is 60%. So, for a meaningful effective lumen gain withprism sheets positioned directly above binned LED chips, the bin depthmust not be chosen arbitrarily.

[0174] The 90-degree prism sheet, usually called BEF (and sometimesVikuiti™ BEF 90/50) is a plastic film product manufactured and sold by3M for brightness enhancement use in the fluorescent backlights commonto all directly-viewed LCD display screens. While 90-degree prisms maybe best for increasing a direct-view display's apparent brightness,90-degrees is not found to be the best apex angle for enhancing thenumber of effective lumens within an LED array illuminator's output beam(see curve 145 in FIG. 7). In this case, the apex angles are increasedto 104 degrees full angle for both the lower and the upper prism sheets.When this is done, total effective lumens rise by an additional 23% to1580 at just about the same bin depth of 174 microns (see curve 145 inFIG. 7).

[0175] BEF is normally used in conjunction with highly scattering whitecavities. The optimum 104-degree prism sheets developed herein are doneso for use with bin arrays whose reflecting surfaces are highlyspecular.

[0176] The detailed physical relationship existing between bin depth 102and prism sheet apex angles 138 and 140 is a very complex one involvingmultiple 3-dimensional reflections between bin sidewalls 106, the LED'sflip-chip's internal structure 118 and the prism facets themselves.

[0177] One way of summarizing the net effect of this relationship forbin depths of 134 um, 154 um, 174 um, 204 um and 234 um is shown in FIG.8, with total effective lumens plotted as a function of the full prismapex angle, made equal for the lower and upper sheets. In this case,peak performance is found to occur in the vicinity of 100-degreesthrough 106 degrees, 176, rather than the more conventional 90-degrees,178, and strong preference is found for bin depths in the vicinity of174 um, 180. As bin depth increases, bin aperture held constant at 1.6mm, sidewall angle 150, γ, decreases, as do the number of totaleffective lumens. As bin depth decreases, sidewall angle increases, andthe number of effective lumens also decrease.

[0178] The peak in total effective lumens that arises in FIG. 8 for 174um bin depth is examined more closely over a range of prism apex anglesbetween 94 and 109 degrees in FIG. 9. Each data point (open square)shown in FIG. 9 represents a computer ray trace run of at least 500,000rays. Despite some small fluctuations, this behavior suggests a regionof relative performance stability for the structure of FIG. 5 with upperand lower prism angles falling between 100 and 106 degrees full angle,176. Performance peaks are found at about 102 degrees (180) and 106degrees (181).

[0179] Yet another way of illustrating this important physicalrelationship is shown in FIGS. 1A-B, also for the illustrative 1.6 mmbin aperture. Total effective lumens is plotted as a function of bindepth for a variety of prism apex angles, from conventional 90-degreesfull angle prisms at the low end, to 106-degree prisms, at the high end.In all cases of prism sheet apex angle, preferred bin depths are foundin the range of 160 to 180 microns, 182.

[0180] F. Uniqueness of Multi-Layered Bin-Prism Sheet Configurations

[0181] The uniqueness of the instant LED illuminator inventions of FIGS.3A-B and 5A-C over conventional lens-based collecting optics can beestimated in the context of the projector example described above.Suppose, just as one example, that light from the 12 mm×9 mm 40-LEDarray is to be collected and then relayed by conventional lenses so thatoutput light satisfies the projector's need for ±12-degrees. In thiscase, it can be shown that the lens used would collect effective lightfrom the array only over about ±25-degrees. Although the 40 LEDs wouldbe generating 4,000 lumens spread evenly over all angles, only 714lumens [(4000)Sin² (25)] would be contained within ±25-degrees. Hence,gains due to the present invention's use of uniquely sized bins (134 and174 microns, FIG. 7) would be more than 40% over this performance. Gainsdue to the present invention's use of uniquely sized bins withconventional 90-degree prism sheets would be over 70%. And, gains due tothe present invention's use of uniquely sized bins with correspondinglyoptimized 102-106-degree lumen enhancement prism sheets would be over100% (or 2×).

[0182] The unique performance of the bin array—prism sheet combinationwill be explored even more thoroughly below in section 2.2.6.2.

[0183] G. THE Effects of Prism Sheet Structure and Other Modifications

[0184] Several structural variations may be made to basic prism sheets88 and 92 (FIGS. 3A-B and 5A-C). One variation involves adding sphericalor aspheric curvature to the prism facets (89 in FIGS. 5A-C) themselveson lower prism sheet 92, upper prism sheet 88, or both. A secondvariation involves adding optical surface structure 142 and 144 to theupper and lower prism sheet substrates 161, this structure being eitherprismatic facets or lenticular cylinder lenses of structural depth 160(lower sheet 92) or 164 (upper sheet 88). None of these additions,however, included alone or in combination are found to have a positiveeffect on total effective lumens. There is one exception. The additionof spherical cylinder lenses 142 and 144 to the prism sheet substratesis found improve the beam's overall spatial uniformity, as will beillustrated later in a treatment of beam uniformity.

[0185] H. Beneficial Effects of Polarization Recycling

[0186] One of the several possible polarization recycling and conversionmechanisms included within the present invention is illustrated in FIG.11. Only a single LED array element in the larger array is shown forpurposes of clarity. In this case, we depict a shallow, tapered-sidewall106 reflecting bin 82, containing a flip-chip LED 118, below a filmstack that includes a set of prism sheets 159 as in FIGS. 5A-C (firstprism sheet 92 and second prism sheet 88), quarter-wave phaseretardation layer 86, and reflective polarizing layer 84. In thisexample, reflective polarizing layer 84 and phase retardation layer 86may be disposed below prism sheets 159, or above them, as shown in FIG.11. The best arrangement depends on the physical properties of thematerials used.

[0187] Generally, most efficient polarization conversion is predictedwhen polarizing layers 84 and 86 are disposed immediately above themetallic reflecting bin and just below prism sheets 159. With thisarrangement, prism sheets 159 must be made of a non-birefringentmaterial free of non-uniform stresses, so as not to cause subsequentdepolarization. Disposing the polarizing layers above the prisms sheetsminimizes chances for depolarization, but potentially increases thenumber of re-cycles necessary before gain is increased. The morecollective re-cycles required for successful angular and polarization,the more power lost from the rays from collective absorption andscattering.

[0188] The polarization recovery mechanism is explained by following twoof many possible illustrative ray paths for the latter case where thepolarization converting layers are above the prism sheets. Thepolarization of any ray segment is summarized in the polarization key atthe bottom of FIG. 11 with three parallel lines signifying anun-polarized ray, a single dotted line signifying linear s-polarization,a double dotted line signifying left hand circular polarization, aseries of circular dots signifying right hand circular polarization, anda single solid black line signifying p-polarization.

[0189] As a first example, consider one random ray 190 generated withinthe LED's epitaxial layers at spatial point A that passes throughsapphire substrate 120. Un-polarized ray 190 then refracts out of thesapphire substrate into the bin's dielectric encapsulant 101 asun-polarized ray 192. Ray 192 proceeds sequentially through air-gap 150prism sheet 92, prism sheet 88, quarter-wave retardation layer 86 andreflective polarizer 84, as un-polarized rays 194, 196, 198, 200, 202,and 204 roughly as shown. Separation of s and p linear polarizationstates takes place at reflective polarizer 84, with p-polarized ray 205transmitted as output, and s-polarized ray 206 reflected back generallytowards LED 118 from whence it came. As ray 206 passes throughquarter-wave phase retardation layer 86, its polarization state changesfrom linear to circular (i.e. from s-polarization to left hand circularpolarization), as ray 208. Circularly polarized ray 208 then propagatessequentially back through upper prism sheet 88, lower prism sheet 92,air-gap 150, encapsulant 101, and sapphire substrate 120 as rays 210,212, 214, 216, 218, and 220 respectively. When circularly polarized ray220 strikes the LED's metallic electrode mirror 125, however, itsundergoes the traditional orthogonal change in circular polarizationstate, becoming right hand circular polarized reflected ray 222. Ray 222then returns through bin encapsulant 101, air-gap 150, lower prism sheet92, and upper prism sheet 88, as rays 224, 226, 230, and 232, followingdeterministic physical trajectories set forth by the laws of reflectionand refraction in substantially homogeneous media. As right handcircularly polarized ray 232 passes through quarter-wave phaseretardation layer 86, it converts from circular to linear polarization,becoming p-polarized ray 234 (exactly orthogonal to re-cycleds-polarized ray 206. As such p-polarized ray 234 passes throughreflective polarizer 84 with minimum loss as p-polarized output ray 235,as it has been oriented for maximum transmission of p-polarized lightand maximum reflection of s-polarized light.

[0190] In this context, un-polarized ray 204 was split about equallyinto linearly polarized rays 205 and 206, but only p-polarized ray 205is useful in polarization sensitive LCD projection systems. Ordinarily,half the delivered lumens in ray 204 are blocked from output use in suchsystems. Yet, in this case, blocked rays like ray 206 are recycled backinto the bin array so as to emerge converted in their polarization asincremental p-polarized output.

[0191] Another illustrative ray trajectory is given in FIG. 11 startingat spatial point B as un-polarized ray 240. Ray 240, unlike the previousillustration, strikes the bin's metallic sidewall 106 as ray 242 beforeleaving the bin. Reflected ray 244 remains un-polarized, and proceedsoutwards as before, as rays 246, 248, 250, 252, and 254. On reachingreflective polarizer 84, polarization separation occurs once again,outputting p-polarized ray 255, and re-cycling s-polarized ray 256. There-cycled ray 256 propagates back through the system, as before, as rays258, 260, 262, 264, 266, 268, 270, 272, 274, 275, 276, 278, and finallyre-cycled p-polarized output ray 280. As with the ray starting frompoint A, the key to efficient recovery of the re-cycled s-polarized rayis linear to circular polarization conversion at quarter-waveretardation layer 86 and left hand circular to right hand circularpolarization conversion at metallic reflector 125.

[0192] Efficient polarization recovery of re-cycled rays such ass-polarized rays 206 and 256 depend on their return paths through thebin array system 82 involving an odd number of metallic reflectionsalong the re-cycling path. There is no such restriction on the number ofmetallic reflections made on the initial path outwards from LED 118. Anyre-cycled rays that involve an even number of metallic reflections,always return to reflective polarizer 84 as s-polarized light, and arethereby remain trapped into making multiple return cycles, until theirtrajectories have been disturbed to the point that they effect a returncycle having an odd number of metallic reflections.

[0193] The system depicted in FIG. 11 is enhanced by even a small degreeof spatial randomness, such as the random surface-slope variations thatexist on all real material surfaces. A forthcoming section is devoted tothe issue of surface randomness and its beneficial effect on theefficiency of re-cycling in general.

[0194] Reflective polarizer films, such as DBEF™ as manufactured by 3M,have been used primarily in conjunction with “white” recycling cavitieswhere polarization conversion develops randomly by completedepolarization of recycled light by random diffusive scattering. In thepresent invention, the recycling mechanism is provided almost entirelyby the specular metallic (and dielectric) surfaces of and within binlayer 82 (FIGS. 5A-B) and flip-chip LED (FIGS. 6A-C). Phase retardationlayer 86 disposed below reflective polarizer 84 and above metallic binarray 82 assures successful polarization conversion when an odd numberof metallic reflections are made during the recycling process.

[0195] The wide and shallow bin structure of FIGS. 5A-B is particularlywell suited to efficient polarization conversion in that very fewsidewall reflections are required before re-cycled polarization isconverted to transmissive output.

[0196] In general, a reflective polarizer increases the percentage ofone linear polarization state with respect to the other by transmittingas output the preferred state and reflectively re-cycling the orthogonalstate. Once recycled, light of the orthogonal state may be converted tothe preferred state, and thereby made eligible for transmission as extraoutput light.

[0197] Without reflective polarizing layer 84 and polarizationconverting layer 86, output light is essentially un-polarized, which isideal for many general polarization-independent lighting applications.Other lighting applications, such as LCD-based video projection, need asmuch pure output polarization as possible.

[0198] I. Second Form: Shallow-Profile Multi-Layer LED Arrays UsingCurved-Wall Reflecting Bins and Modified Prism Sheets

[0199] The second form of the present invention is very similar to thefirst, but uses contiguous bins having curved rather than flatsidewalls. The sidewall shape of reflecting bins 82 shown as being flatin FIGS. 5A-B may have any mathematically specified curved profile, asfor example that shown in FIGS. 2A-B. Just as with the straight-walledreflecting bins illustrated in FIGS. 5A-B, mathematically shapedsidewall curves are another closely related way of introducing a meansof control on reflective interactions with over-lying prism sheets. Onebenefit from choosing mathematically shaped sidewalls is that theangular distribution of the bin's output light can be more tightlycontrolled within the angular range of interest than with moststraight-walled bin configurations.

[0200] There is one important class of mathematically shaped sidewallsthat have the ability to alter angular distribution while minimizing thenumber of sidewall reflections any light ray experiences within eachbin, input and output apertures. Bins of this type are generally knownin prior art as non-imaging concentrators (and sometimes as compoundparabolic concentrators or CPCs). Bin arrays made with bins having theseideally shaped sidewalls behave as θ_(i)/θ_(o) transformers, in thateach bin within the array transforms LED input light of maximum angle 0;to output light of maximum angle θ_(o) by virtue of the well establishedSine Law: A_(i) Sin²θ_(i)=A_(o) Sin²θ_(o), where A_(i) is the area ofeach individual emitting region, A_(o) is the area of each individualoutput aperture, and θ_(i) and θ_(o) the respective input and outputhalf angles. Optical systems designed to preserve across each aperture,the product of aperture area and extreme angle, are known do so with thehighest possible lumen transfer efficiency. When this principle isapplied to bins such as those of layer 82 in FIGS. 5A-B that are made ofor filled with dielectric media 101, the extreme output angle θ_(o)predicted by the Sine Law exists at within the output aperture of everybin, but just inside the bin's media. It is this calculated extremeangle just inside the bin medium that determines, by Snell's Law at thedielectric-air interface, the full angular range of output light emitted(or extracted) from each bin.

[0201] One way such curved-wall bins can be used advantageously is totransform the LED's ordinary ±90-degree input emission into outputangles confined to or about ±θ_(c) within the bin's dielectric media 101(FIGS. 5A-B), θ_(c) being the critical angle for the bin'sdielectric-air interface. When this bin design is used, it becomespossible to extract all light emitted by the LED substrate intosurrounding dielectric media 101. Ordinarily any light arriving at thebin aperture at angles having trajectories higher (or greater) than±θ_(c) remains trapped in the bin's dielectric media by total internalreflections.

[0202] As an example of this, consider the following scenario. Adielectric fill medium 101 (FIGS. 5A-B) nominally of illustrativerefractive index, n=1.49, has a critical angle of θ_(c), θ_(c) beingSin⁻¹ (1/n)=42.16 degrees. In the X-meridian, and using an illustrativeinput aperture size of 1.1 mm, the Sine Law specifies that thecorrespondingly ideal output aperture size is 1.1/Sin (42.16)=1.64 mm.This aperture value is close to the preferred output aperture size asused above for straight walled bins. Bin depth, in this curved sidewallcase, however, must be made considerably deeper, as prescribed by themathematically derived length of an ideal non-imaging concentrator,L=0.5(X_(o)−X_(i))/Tan θ_(o), or 1.5 mm (which is 8.5 times deeper thanthe required depth of the tilted flat side-walled bins of FIGS. 5A-B.

[0203] Despite the higher output coupling efficiencies possible withcurved rather than straight walled reflecting bins, performance benefitsare limited to applications where the illumination aperture is nototherwise restricted in area, as it is in the case of an imageprojector. When the overall bin array is limited to the rectangular areaof the projector example, the number of bins fitting within thisaperture is limited mathematically, as in equation 4.

N _(BINS)=(X _(ILL))(Y _(ILL))/(X _(BIN))(Y _(BIN))   (4)

[0204] For example, when X_(ILL) is 12 mm and Y_(ILL) is 9 mm, and thebin's output aperture is square and 1.6 mm on a side, there can be 42bins in the array. When the bins are shaped so as specifically to narrowthe range output angles, for example from ±43.4 degrees to ±38 degrees(within the dielectric), aperture size increases from 1.6 mm to 1.97 mmand maximum number of bins fitting in the 12 mm by 9 mm array aperturefalls from 42 to 34. The fewer the number of bins, the fewer the numberof LED chips its possible to use, and thereby the lower is the totaleffective lumens that are developed.

[0205] This behavior can be seen in FIG. 12, which plots total outputlumens contributed by individual bins versus half-angle of the bin'soutput light in air. The validated computer model described above isused for this purpose. Curves 163, 165 and 167 are for the curved-walledbins by themselves, without any prismatic over-layers such as layers 88and 92 in FIGS. 5A-C and 11. These curves related performance for outputangles within bin's internal dielectric medium 101 of ±43.2, ±30 and ±20degrees respectively (corresponding to angles in air of ±90, ±48 and ±30degrees). Notice in the case of curve 167 that maximum lumen output inair is reached close to an included half-angle of 30 degrees, asexpected. Reference curve 161 in FIG. 12 is for the case of 1.6 mmsquare straight-walled bins described in the above sections; includedfor purposes of easy comparison.

[0206] The legend for the plots of FIG. 12 summarizes salientcharacteristics of each curve. Designation A refers to the point oncurve 161 at an output angle of ±25 degrees in air; designations B, Cand D refer to corresponding points on curves 163, 165 and 167. Noticethat curves 161 and 163 are quite similar. This is quite expected as the174-micron deep straight-walled bin of curve 161 has been optimized (inFIG. 7) to behave in reasonably close approximation to the nearly ideal1.5 mm deep etendue-preserving curved-wall angle-transforming design163. In both cases, each bin type outputs into the air above the binapertures, about 23-25 lumens of the 100 lumens per bin possible (within±25 degrees); and about 93 lumens of the 100 possible (within the full±90 degrees). This equivalency exists only for equally sized binapertures. As the curved-wall bins are shaped to concentrate outputlight more tightly, their bin efficiency rises to 40 lumens for ±30degrees in air (point C) and to 73 lumens for ±20 degrees in air (pointD), but so does the corresponding size of their bin aperture (2.2 mm and3.2 mm square, respectively). As bin size increases, the number of binsable to fit in the fixed 12 mm by 9 mm array decreases significantly; 22bins for 40% efficiency, and 10.5 bins for 73% efficiency.

[0207] All data in FIG. 12 is for the bins by themselves. Thecomparative effects of adding prism sheets 88 and 92 above the bins areconsidered in the next section.

[0208] J. Performance Comparison Between Straight and Curved-Walled BinArrays Using Modified Prism Sheets

[0209] Total output lumens between ±25-degrees for straight-walled binarrays is shown in FIG. 8 as a function of bin depth and prism apexangle. For curved-walled bins, bin depth depends on aperture size, sothere is only one performance curve for the comparable aperture'size of1.6 mm.

[0210] Performance comparisons must be made using identical angularranges and identical illumination apertures. Choosing such conditionsfor comparison depend on the particular application. For videoprojectors, the etendue relations of equations 1 and 2 are not the onlyboundary conditions involved. When an additional stage of angletransformation is used, such as the pseudo-Kohler transformer describedin our previous invention, additional conditions come into play. Thebasic geometry of the planar LED array source 300 as integrated with apseudo-Kohler second-stage angle-transformer 308 is summarized in FIG.13.

[0211] It is this second stage of angle transformation, or itsfunctional equivalent, that provides efficient interface (or coupling)between LED array 300, its physical aperture 302, and aperture of use304, in this example, an LCD 306. The angle transformation means is anoptical focusing or condensing system (that can be either a lens ormirror) 308, whose effective focal length 310, FL, is ideally matched tothe positions of LED light source panel array 300 and LCD 306. Whenlight source array 300 and LCD 306 are positioned coaxially (so asproviding telecentric illumination for any imaging system used to viewor project the LCD image) and each are at the respective equivalentfocal planes 312 and 314 of condensing system 308, spatial uniformity ofthe angle-transformed light conveyed across LCD aperture 304 ismaximized, as has been described previously.

[0212] Field coverage on the targeted LCD (or DMD) in the projectionexample is forced solely by illumination angle, θ_(ILL), 322, andspecifically by the center point ray 324 along with its resulting ray326 after focusing action of condensing element 308. Ray 326 strikes theedge of the output target (LCD or DMD) 306 in each meridian. All higherangle rays 328 emitted by LED array source 300 do not reach target 306in a useful manner (either by missing condensing element 308 altogether,or by causing a larger than useful output angle 320 at the target), andare potentially wasted. (Novel mechanisms for re-cycling and re-usingunused rays 328 will be discussed below.)

[0213] One advantage of the light source arrays 300 of FIGS. 3A-B, 5A-Cand 11 in this regard is that while increasing the lumens produced atlower angles at the expense of those produced at higher angles, theilluminator's overall output extends smoothly over the entire angularrange. This means that field coverage on LCD (or DMD) 306, regardless ofits particular aspect ratio, is automatic.

[0214] Geometric relationships imposed by the angle transformationsystem of FIG. 13 are controlled by triangles 316 and 318, also shownshaded (and enlarged) for greater clarity. Upper triangle 316 iscontrolled by maximum angle 320, ω_(LCD), allowed for light processed byLCD (or DMD) 306. As in the ongoing projector example, this angle isroutinely fixed at the ±12-degrees in air (±8-degrees in transparentdielectric media of refractive index 1.49) associated with f/2.4projection systems. [NOTE: The use of f/2.4 as a working example hasbeen predicated by limitations imposed by existing mirror travel allowedwith digital micro-mirrors in DMDs and by the steep fall-off in contrastratios prevalent in current micro-sized LCDs when their illuminationangles exceed ±12 degrees. While mirror swing in DMDs may be afundamental limitation, the image contrast sensitivity to illuminationangle in LCDs may be improved by a variety of means now well known inthe larger format LCDs used in laptop computers and desktop monitors.Should any equivalent angle-widening means be developed for micro-sizedLCDs and/or the optical systems within which they are used, similarexamples of the current inventions could be made for f/2.0 (±14.5degree) and even f/1.7 (±17 degree) projection systems without seriousreduction in image contrast.]

[0215] Lower triangle 318 is controlled by the size of LCD aperture 304in each respective meridian (X and Y). Combination of these twogeometric conditions results in the expression given in equation 5,which is a variant in each meridian of equations 1 and 2. Thisexpression can be generalized to any other LED array lightingapplication using the same angle transformation method of FIG. 13.

X_(ILL) Tan θ_(ILL)=X_(LCD) Tan ω_(LCD)   (5)

[0216] While using such a pseudo-Kohler (focal-plane-to-focal-plane)optical coupling method is quite well established in general practices,its specific embodiments with the unique close-packed LED light sourcearrays of FIGS. 1A-B, 2A-B, 3A-B, 5A-C, and 11 are not. Moreover, itwill be shown later that such an arrangement is in fact preferable forcoupling light efficiently from planar light source arrays (such as LEDarray 300) to planar illumination targets (such as LCD 306).

[0217] In projector system usage, X_(LCD) and ω_(LCD) are fixed bydesign intent, so the product of illumination size and the maximumillumination angle allowed are defined by equation 5. When X_(LCD) is24.384 mm (as in a 4:3 aspect ratio aperture with 1.2 inch diagonal),and ω_(LCD) is 12 degrees (as in the f/2.4 example), the product ofilluminator size and angle has to be about 5.183 as opposed to 5.07given by the Sine Law. At ±25-degrees, the Sine Law limited illuminatorsize is slightly larger than that governed by the Tangent dictatedgeometry of FIG. 13. In real system examples, these relations alsodepend on the refractive index of any dielectric media placed betweenlight source panel array 300, focusing system 308 and LCD panel 306. Inmany of the designs described in the earlier invention, these spaces maybe advantageously occupied with dielectric beam-splitting cubes havingrefractive index about 1.49. When this is assumed to be the case, itaffects the values of the effective focal length 310 (and 311) as wellas illumination angle, θ_(ILL), 322. The optical direction cosinesmaintain preservation of etendue across every dielectric-air boundary,but the physical path length (and angle) of light in refractive mediadiffers by that in air by means of Snell's Law.

[0218] When the output apertures of curved-wall and straight-walled binsare made the same and set, for example, at 1.6 mm, performancecomparisons are made fairly. In each case, the same number of LED chipsand bins fit within the allowed illumination aperture 302 in FIG. 13.Using equation 5 and the effective illumination angle (±25-degrees) forfull field coverage, the illumination aperture is 11.62 mm by 8.71 mm,and there are about 40 bins per aperture. Total effective lumens arethen plotted in FIG. 14 as a function of apex half-angle (β₁=β₂) for theprisms used in sheets 88 and 92, for both 174-micron deepstraight-walled bins and for 1.5 mm deep curved-wall bins.

[0219]FIG. 14 shows, under these conditions, that the performance of thestraight-walled bins exceeds that of the deeper curved-wall bins byabout 12%, throughout the range of prism angles considered. While theremay be more advantageous combinations of curved-wall bins and prismsheets for other applications, the use of straight-walled bins ispreferred for the system of FIG. 13. This is convenient, as fabricationof shallower straight-walled bin arrays is easier than deeper,curved-wall bin arrays.

[0220] K. Re-Cycling and Re-Use of Optical Flux from LED-Filled BinArrays

[0221] Re-use of re-cycled LED output light from each bin in the arrayis fundamental to increasing efficiency in the instant inventions ofFIGS. 1A-B, 2A-B, 3A-B, 5A-C and 11. Prism sheets 88 and 92 transmitoutput light from bins 82 only at certain allowed angles where raytrajectories though the two prism layers suffer no total internalreflections that return potential output light to the bins from whencethey came. Generally speaking, total internal reflection returnsaffected rays backwards towards bin array 82 just as s-polarized lightrays were made to return from reflections at reflective polarizer 84 inFIG. 11. While the polarization recycling mechanism of FIG. 11successfully converts the blocked polarization state to the transmittedpolarization state in a single round trip because of the actions ofdielectric polarization conversion layer 86 and metallic polarizationconversion layers 106 and 125, successful conversion of total internallyreflected light rays, whether polarized or un-polarized, depends onthere also being a means of angular randomization, such as the surfaceslope microstructure mentioned earlier.

[0222] Prior to examining the means of optical path randomization thatfacilitate most efficient re-use of re-cycled light rays, we introducesome additional re-cycling mechanisms and configurations.

[0223] L. Hemispherical Re-Cycling Mirrors in Pseudo-Kohler AngleTransforming Illumination Systems (as in FIGS. 15A-E and FIGS. 16A-D)

[0224] Hemispherical mirror 332 is added to the instant invention ofFIG. 13 as in FIGS. 15A-E to collect and redirect high-angle lightoutput such as 334 from LED light source array 300 that would otherwisehave been wasted.

[0225] The focal point of sphere 332 lies at its center of curvature,point 301 in FIG. 15A. Any light emanating from (or near) this point 301that strikes the sphere's inside reflective surface, returns to (ornear) the center point 301 from whence it came. Hence, the reflectingsphere (or in this case, reflecting hemisphere) functions as a recyclerof light emanating from the vicinity of its center.

[0226] The pseudo-Kohler angle transformation system of FIG. 13 onlyprocesses light rays passing through the physical aperture of condensingelement 308 like illustrative ray 354. Higher angle rays like 334, 338and 355 which travel beyond this aperture, are lost from use. Hemisphere332 provides a means for recovering them reflectively. Considerillustrative high-angle ray 334 originating approximately from thegeometric center of LED array 300's output aperture 302. Since focalpoint 301 of hemispherical mirror 332 is positioned at this point 302,wide-angle rays like 338 are reflectively returned back along theiroriginal out-going path. As another example of this return mechanism,consider LED output ray 338 leaving left hand edge-point 337 of LEDlight source array 300. Ray 338 reaches hemispherical mirror 332 at itsinside point 336, and returns after reflection along a geometricallypredictable if not exactly identical optical path, to light source 300at its corresponding right hand edge point 339. Only slope errors onmirror surface 332 interfere with precise optical return within arraysource 300.

[0227] The symmetrical geometry described by rays 334, 338 and 340dictate that out-going ray 338 from a left edge bin in array source 300a specific distance, X_(ILL)/2 from light source center point 301,returns as ray 340 to an edge bin on the opposite edge of the array, anequal distance from the array's center point. This geometry is true forparaxial rays such as those illustrated in FIG. 15A, as well as the morecomplicated out-of-plane skew rays.

[0228] FIGS. 16A-D show four different perspective views 340 ofhemispherical mirror 332 in wire-frame style. Top-view 342 (FIG. 16C)shows the square aperture cutout required for condensing lens 308 andthe passage of all effective output rays. Side view 346 (FIG. 16B) showsthe effect that square cutout 344 has on the mirror's surface area.Perspective views in FIGS. 16A and 16D show the effective mirror surfacemore clearly. Nominal mirror radius, R, 319, is chosen by the geometryof triangle 318 in FIGS. 13 and 15A as being R=FL/Cos θ_(ILL).

[0229] Light source 300 as depicted most generally by symboliccross-sections in FIGS. 15B-E, can be any one of a number of square,rectangular or circular light source emitting apertures. Some, but notall, practical examples include the flat-walled (or curved-wall) binarrays of FIGS. 3A-B and 5A-C combined with lower and upper prism sheetsas 90 in the present invention, the flat-walled (or curved-wall) binarray 82 used alone in the present invention, an individual flat-walled(or curved-wall) bin 350 (including the case, not illustrated, of lowerand upper prism sheets) of the present invention, and/or one or more ofthe commercially-available discretely packaged LEDs 352, such asmanufactured by LumiLeds under the trade name Luxeon. For highest outputapplications, light sources that are structured as 82, 90 and 350 arepreferred as structures maximizing lumens per mm².

[0230] M. Fresnel-Type Hemispherical Re-Cycling Mirrors in Pseudo-KohlerAngle Transforming Illumination Systems (as in FIGS. 17-18)

[0231] A more compact and spatially efficient form of hemisphericalre-cycling mirror 332 as used in FIGS. 15A and 16A-C is shown inwire-frame perspective 370 in FIG. 16D and in system cross-section inFIG. 17. In this form of the invention, hemispherical re-cycling mirror332 of FIGS. 16A-C is cut into n hemispherical slices such as forexample, 4^(th) slice 372 in FIGS. 16D and 17. Cutting these slices isakin to making a pseudo-cylindrical Fresnel-type mirror. One of manypossible design methods used to construct the form of ringed reflectiveelement 374 is to constrain the imaginary inside diameter D_(c), 376, ofa cylindrical tube as being that of the bounding circle surroundingcondenser element 308's spatial outline 344 (as in FIG. 16D and FIG.17). In this case, the inside facets 376 of what is to be acylindrically faceted reflecting tube, contain thin highly reflectingfront-surface metallic coatings (such as enhanced aluminum or protectedsilver).

[0232] One possible example of the instant invention is the 7-ringmirror design with pseudo Fresnel facet angles as shown in thecross-section of FIG. 17. Rather than using a single hemisphericalradius value for each ring, as would more normally be the case with astandard Fresnel design, the facet radius is set at a different valuefor each succeeding ring. Either way, an appropriate Fresnel-typehemispherical reflective re-cycling tube results, as in FIG. 17.

[0233] The 7-ring configuration of FIG. 17 is developed along thefollowing geometric arguments. Meridian edge lengths for condenser lens308 are taken as CLX and CLY, with diagonal length CLD determined bygeometry. For simplicity, each ring 372 is given an equal ring height,RH. LED illuminator array 300 is considered with equal X and Y meridianedge lengths, XILL. The upper and lower focal lengths FL1 and FL2 ofcondenser lens 308 have values in the instant invention that depend onthe media in regions 380 and 382 (equal media, equal values), theaperture size of imaging device 306, and the physical space neededbetween imaging device 306 and condenser lens 308. As a starting point,the center of curvature for each ring section is located at center-point384 of light source aperture 300. Other focal points, or a differentfocal point for each section may be considered as well as a means offine-tuning the re-cycling distribution. Inside tube diameter 374 ismade no smaller than the condenser lens's diagonal length CLD. Theradius, R_(N), for each n^(th) ring section in this illustrativeconstruct, N being equal 1 to 7, is given in equation 6.

R _(n)={square root}{square root over (((N)(RH))²+(CLD)²)}  (6)

[0234] One low profile supporting tube shape for the 7 ring sections isshown in trapezoidal cross-section 386. Such a supporting shape orsubstrate for the reflecting rings becomes slimmer as the number of ringsections increase. The entire structure 370 can be molded in plasticsections (halves or thirds), and then snapped together, or moldedcompletely using a dynamic injection mold to permit extraction of theotherwise captured molded part. If, as one numerical example, X_(LCD) is24.384 mm, FL₁ is 39.54 mm and filled with a medium of refractive index1.49, FL₂ is 26.21 mm in air, X_(ILL) is 12 mm, then CL_(X) is 35.54 mm,CL_(Y) is 29.46 mm, CL_(D) is 46.16 mm, and for 6 mm ring section heightRH, the successive ring radii are 46.54, 47.69, 49.55, 52.03, 55.05,58.54, and 62.41 respectively.

[0235]FIG. 18 shows an analogous if fundamentally different reflectivere-cycling structure also disposed about the interior rings of anessentially cylindrical form 390. In this related construct of theinstant invention each of the illustrative 13 ring sections contain acircular array of corner cube reflectors such as 392 whose optimumpointing direction has been aimed so that the ray bundle within eachcorner cube's aperture is retro-reflected generally back along thedirection of incidence. This requires separate aiming of the cornercubes in each successive cylindrical ring section.

[0236] N. Factors Affecting Efficient Re-Use of Re-Cycled Light

[0237] Whether the re-cycling of light from light source 300 is causedby total internal reflections within prism sheets 88 and 92, reflectionfrom hemispherical reflector 392, reflection from the ringed facets ofFresnel-type hemispherical reflector 370, the return light from cornercube type retro-reflector 394, or any equivalent form of return, thelight ray directions that so return to the interior of source 300 fromwhence they came are in the wrong angular directions for subsequentre-transmission as usable incremental output. Unless a means existswithin light source 300, is artificially provided within or external tolight source 300, to change the out-going angular directions of lightreturned, there can be no net increase in the total light output of thesystems of FIGS. 3A-B, 5A-C, 11, 13, 15A-E, 17, or 18. For there to be anet output light increase, some angle-changing mechanism needs to beintroduced. The collective optical light paths of returning light mustnet a sufficiently large change in angular direction so thattransmission through condenser element 308 is permitted.

[0238] One potential angle-changing means that can be invoked is there-passage of return light through the physical structure of lightsource 300, including all reflections, refractions and diffractionsinvolved. In this case, the light source arrays reflecting bins serve asrandomizing cavities. Since the return path of recycled is not exactlythe same as the original output path, return to light source 300typically takes place with a spatial offset from the point of origin.Because of this spatial offset, the net effect on output angle ofrecycling through light source 300 can be quite different. Ray 338 inFIG. 15A originated within a reflecting cavity on the left hand side ofthe array, but returned as ray 340 to a reflecting cavity on the righthand edge.

[0239] Despite this spatial offset, the collective change in angulardirection must be large enough that the re-cycled output light passesthrough prism sheets 88 and 92 if present, in such a way that theultimate output transmission occurs somewhere within the aperture ofcondenser lens 308. The chances for favorable angular conversion areencouraged in the following ways.

[0240] FIGS. 19A-B show the basic schematic cross-section of oneillustrative LED-containing bin element 400 within the instant inventionincluding bin array layer 82 (FIG. 19B showing a magnified portion ofthe bin sidewall). This same general structure appears in FIGS. 3A-B,5A-D and 11, as well as within the generalized light source 300 of FIGS.13, 15A-E, 17 and 18. All major surfaces (and interfaces) shown incross-section 400 have been drawn with smooth and regularspecularly-reflecting surfaces, smooth and regular refractinginterfaces. Under these pristine circumstances the path of emitted ray402 is completely deterministic. Ray 402 passes though sapphiresubstrate 125, optical encapsulating medium 101 as ray 404, and thenoutwards as ray 406 into the medium above bin 400 (typically air).Perfect Snell's law refraction occurs at points 408 and 410, thesubstrate/fill medium boundary and fill medium/air boundaryrespectively. Upon reflective return via the reflective re-cyclingmechanisms described above, corrected in energy by the losses due toeach reflection, this ray returns displaced some distance from itsout-going trajectory 406, as ray 412. The return location of thisparticular trajectory is only approximate, and just for illustrationpurposes. Nevertheless, it can be seen that despite refractions andpoints 414 and 422 and reflection at point 416, ray path segments 412,418, and 420, at least in this case, do not result in a substantialoutput ray 424 direction different than incoming return ray trajectory412. For as long as this situation remains so, and for however manyreturn cycles there are between bin 400 (or any neighboring bins 400),there will be no effective net contribution to the system's usefuloutput light.

[0241] Changing the course of this outcome requires introduction ofstructural randomness.

[0242] O. Structural Randomness and Recycling Efficiency (as in FIGS. 20and 21A-E)

[0243] One form of structural randomness is generated by encouraging thepresence of continuous surface slope errors 432 about the averagesurface slope, as in FIG. 19B detail 430 (showing just one of severalpossible highly magnified examples, the rippled micro surface on binsidewall 106). Such slope errors, generally no greater than about ±5degrees, often occur naturally as macro or micro imperfections createdduring surface formation. Such micro features can be introduceddeliberately. In either case, the effect on recycled light illustratedin FIGS. 19A-B operates in combination with ordinary reflections andrefractions to increase the net change in angular re-direction. Suchsurface imperfections are explicitly distinguished from the rougher andmore abrupt surface imperfections that scatter light rays over a ±90degree angular range. While scattering surfaces increase chances forsuccessful angular conversions, they also can prevent otherwisesuccessful output rays from escaping in the first place.

[0244] Non-scattering microstructures are the gentle depressions ordimples in surface slope brought about by physical surface deformationscaused by impingement of spherical particles. One process foraccomplishing this is known as liquid honing wherein spherical particlesare contained within a liquid flow. Another means for this is themachining (or gentle etching) of surface relief patterns into thesidewalls 127 of form tool 128 as in FIG. 4B. Such patterns made in theforming tool, are transferred to the molded or embossed part FIG. 4A.

[0245] One example of the effect of structural randomness is given bythe behavior of illustrative return ray 418 as shown in FIG. 19B, detail430. This incoming return ray 418 reflects from the flat average surfaceat point 416 about surface normal 434. Dotted ray trajectories 420 and424 represent the normal optical path were the surface flat, as shown inthe top view. When the local microstructure at point 416 results insurface normal 440 tilting by 5 or more degrees with respect to originalsurface normal 434, reflected ray 442 and its reflected output component446 are themselves tilted by an equivalent amount, in this case, closerto the preferable output direction.

[0246] The more (high-efficiency) surface reflections and refractions areturn ray makes during its travels through bin 400, the more deviatedthe resulting output ray can become from its otherwise idealizedtrajectory.

[0247] A degree of angle changing on critical optical interfacesincreases the percentage of re-use possible. As a result, one group ofrays will return further outside the preferred output acceptance range,while another group will return closer to, or within, the preferredacceptance range. As with the earlier system performance analyses ofFIGS. 7-10 and 12, predicting the magnitude of such net improvementrequires either direct experimentation, which is cumbersome andexpensive, or the equally predictive realistic computer model describedabove. Skew rays and the chances for multiple reflections andrefractions complicate analytical predictions.

[0248] Angle-changing microstructures can be applied with similar (orgreater) benefit to media/air interface 406, sapphire interfaces 450 and452, and the LED's reflective return mirror 125.

[0249]FIG. 20 shows another schematic cross-section of bin 400, thistime illustrating the angle changing effects as they occur inconjunction with lower prism sheet 92. By virtue of microstructureapplied on bin sidewalls 106 (and potentially on the bin medium'sinterface with air), combined with the angle-changing action of theprism sheet, a ray's return trajectory, otherwise blocked by totalinternal reflection within a prism, can be converted to one thatachieves output. Some converted output rays will add to those alreadywithin the preferred angular range (i.e. that which passes through theaperture of condenser element 308). The same will be true of prism sheetoutput rays that exist outside the preferred angular range, and thatreturn to the aperture of bin 400, or any neighboring bin 400, by theretro or hemispherical reflection described previously.

[0250] One example of this particular return mechanism is illustrated inFIG. 20 by the behavior of sequential ray segments 450, 452, 454, 456,458, 460, 462, 464, 466, 468, 470, 472, and 474. On this particularoptical path starting within LED 118, which may have directionalcomponents into (or out from) the plane of the drawing, is such that thetrajectory of ray segment 456 forces an angle with the normal to theprism facet at point exceeding the critical angle for the prism'sdielectric media. Reflected ray segment 458 therefore travels across theprism element and strikes the opposing facet at point 461, where it alsoexceeds the critical angle, thereby producing total internally reflectedray segment 460 whose direction is substantially backwards into the binand LED from which it came. By this return process, emitted LED ray 450fails on its first pass to become part of the system's useful outputlight, but gets another chance, as the ray continues to reflect andrefract within bin 400 via segments 462, 464, 466, 468, 470, 472, and474. This optical path involves refractions at bin points 476 and 482,refraction at prism sheet substrate surface point 484 and reflections atbin sidewall points 478 and 480. The result of this is that prism sheetoutput ray 474 transmits as output within preferred angular range, andthus adds incrementally to the total useful output.

[0251] Without prism sheet 92, and the multiple return reflections andrefractions, the original LED output ray segments 450, 452 and finally454 would have remained outside the preferred angular range.

[0252]FIG. 20 further illustrates the system's collective effect on ageneralized external return ray 490, which is presumed to have reflectedback from, for example, a reflecting facet of the Fresnel-typehemispherical recycling mirror 370 as in FIG. 17. Relatively high angleray 490 traces back through the system of FIG. 20 along ray segments493, 494, 496, 498, 500, 502, and finally as output segment 504. This isjust one of many possible ray trajectory examples of this type. Withoutspatially varied surface microstructure introduced at point 510, raysegment 496 would have reflected along dotted trajectory segment 497,which would have continued outwards along dotted path segments 512, 514,and 516, path 516 heading well outside the preferred angular outputrange, and not substantially improved over the angular direction ofincoming return segment 490. As a result of the surface microstructureat point 510, the actual outgoing ray path segments are successively498, 500 502 and 504, ray segment 504 heading out well within thepreferred angular range.

[0253] The microstructure developed along bin sidewalls 106 may be anygeometry that spatially varies the local surface slope, such as tomention a few, spherical bumps, spherical depressions, sinusoidaloscillations, prismatic growths, prismatic depressions diffractiongratings. Generally, diffuse scattering type surface textures are to beavoided in favor of specularly reflecting or diffractive surfacetextures with smooth or predictable variations in surface slope.

[0254] Similar spatially varying surface modifications are useful oneach of the other material interfaces within bin or bins 300, such asshown in the schematic cross-section of FIGS. 21A-E. Detail 600 in FIG.21E shows a magnification of LED 118 and its integral layers as sketchedin FIG. 6. Transparent LED substrate 120 (sapphire in present flip-chiptechnology) has upper plane surface 602 and lower plane surface 604.Either or both of these surfaces may be altered so as to contain, eitherintrinsically or deliberately, non-scattering and continuously varyingmicrostructure, such as the spherically rippled (or dimpled) structureillustrated. As long as the microstructure depth is sufficiently lessthan the thickness of the epitaxial layers themselves (about a micron orso), and the structural period more than several microns or so,epitaxial LED device layers 122 may grow in conformance with the surfaceslope variations on lower substrate surface 604. In this manner, metalelectrode mirror 125 will also conform to the surface pattern.

[0255] Surface microstructures may also be formed at bin 300'sdielectric-air interface 604 as shown in the magnified details 606 inFIGS. 21A-C respectively. Among the many possible microstructurescontributing spatially varying refraction angles are the sphericallenslets shown in FIG. 21C (alternately spherical depressions), mesas orribs as in FIG. 21B, and prismatic or pyramidal structures as in FIG.21A.

[0256] One ray path example illustrating the combined effect of theseadditional microstructures is also shown in FIGS. 21D-E, starting withhigh-angle return ray 612. As this ray passes back through the binstructure, it encounters potential direction altering mechanisms atpoints 630, 632, 634, 636, 638 and 640. The collective result is thatrecycled output ray 624 has been made significantly different that thanof incoming ray 612.

[0257] P. Angle Re-Cycling with External Re-Use (FIGS. 22A-B)

[0258] In some applications of the instant invention there is advantagein spatially separating the re-use of re-cycled light from anglechanging mechanisms brought about previously within the bins of binarray 300 themselves. Such mechanistic separation is possible, as inFIGS. 22A-B, by adding an external angle-changing optical system 650between light source array 300 and condensing element 308 of FIGS. 15A,17, and 18. One of two cooperating external elements, mirror 650, isused to collect (and then redirect) high angle light rays from lightsource array 300 that would otherwise miss the input aperture ofcondensing element 308. The cooperating optical element, light pipe 654with angle changing optical layer 662, is arranged above array source300, so that it transmits the source's narrow angle output light withminimum optical effect, while simultaneously processing any wider-anglelight that is deliberately coupled into it. Optical layer 662 isconfigured to transmit reasonably collimated light, such as ray 664,without a substantial change in direction. Layer 662, however, isconfigured to behave much differently for more obliquely directed lightsuch as ray 666.

[0259] Q. Collection and Recycling by Means of Elliptical Troughs (as inFIGS. 22A-B and FIGS. 23A-B)

[0260] This light collecting and redirecting means consists of two setsof opposing elliptical reflecting troughs, 652 and 653 plus 670 and 671,arranged in the form of a 4-sided reflecting box made with internallyreflecting sidewalls. Each of the four elliptical troughs have two focallines apiece, one generally in the output plane of light source array300, and the conjugate one position at or near an edge of light pipe654. With regard to elliptical trough 653, the two focal lines are shownas 658 and 660. The focal lines appear as points in the cross-section ofFIG. 22A, and as lines in the perspective view of detail 651 in FIG.22B. Focal line 658, for example, is positioned at or near a centralportion of light source array 300 (for example, the line through centerpoint 301) while the other focal line 660 is positioned at or near oneparallel end face (or edge) of optical light pipe element 654, as shown.(Note, elliptical curves have two related focal points, but ellipticaltroughs have two related focal lines.) In this manner, all lightemanating from light source array 300 at or near the line runningthrough its center point 301 is collected by focal line 658 and coupledvia reflecting surface 653 efficiently through corresponding focal line660 into light pipe 654.

[0261] This collection and re-direction behavior is also traced byseveral illustrative rays 670, 672 and 674 all of which leave lightsource array 300 from the vicinity of its center point 301 at highenough angles that they were destined to miss the entrance aperture ofcondensing element 308. The ray paths shown in FIG. 22A are thoseactually traced by the aforementioned computer model, and the shapesdepicted in FIGS. 22A-B are those actually developed by the computermodel. Ray 670 propagates towards elliptical trough 653 and reaches itat point 680, whereupon it is reflected towards corresponding focal line660 as ray 668. Whether ray 668 passes exactly through focal line 660depends on the exact location of its point of origin within the outputaperture of light source array 300. This particular illustrative raypath 668 actually just misses mathematical focal line 660, but stillsuccessfully enters light pipe 654 through its right hand edge-face 688,and subsequently makes numerous light pipe reflections by total internalreflection. The same behavior is exhibited by lower angle ray 672 thatis reflected by element 653 at point 688 towards light pipe face 688 asray 666. Ray 666 also makes total internal reflections within light pipe654, but they are fewer in number than those resulting from more steeplyangled ray 668.

[0262] FIGS. 23A-B provide a more descriptive cross-sectional view ofthe invention of FIGS. 22A-B showing its complete positioning within theprojection system of FIG. 13. Opposing elliptical mirrors 652 and 653are rendered as solid-lined segments of equivalently tilted ellipses 676and 675. A perspective view of mirror 652 is added for clarity.Elliptical curves 675 and 676 have been rotated in the plane of thecross-section FIG. 23A about common their focal line 658, which has inturn, been made to lie in or near the output aperture plane of lightsource array 300. The degree of rotation between elliptical curves 675and 676 is established by the coincidence of each secondary focus (660and 661) with opposing edge faces (685 and 688) of light pipe 654. Thiscoincidence depends geometrically on the elevation H of light pipe 654above light source array 300. As in FIG. 13, the distances betweenplanar light source 300, condensing element 308 and spatial lightmodulator 306 are set by the corresponding upper and lower focal lengthsFL₁ and FL₂ (which are equal unless the refractive index of thecorresponding media are different).

[0263] R. Re-Use and Recycling by Means of a Light Pipe (as in FIGS.22-25)

[0264] None of the rays coupled to light pipe 654 through any of itsfour edge-faces (683, 685, 687 or 688) are able to enter the aperture ofcondensing element 308 without some cooperative out-coupling action bylight pipe layer 662.

[0265] Several preferable forms of light pipe 654 are shownschematically in FIGS. 24A-C, including slab 700 (FIG. 24A), slab withsharply beveled edge 702 (FIG. 24B), and slab with slowly tapered edge704 (FIG. 24C). The slowly tapered edge 706 OF FIG. 24C may beconfigured as an ideal angle transformer, efficiently colleting up to±90-degrees of input light to the approximately ±42 degrees appropriatefor total internal reflection within a light pipe. Slab structures 700,702 and 704 may include out-coupling layer 662 on either or both theirupper or lower faces, while not within the region of their couplingedges.

[0266] Specifically, light pipe layer 662 is arranged, selectively, tocounteract the light pipe's prevailing conditions of total internalreflection, and in doing so, re-direct otherwise trapped rays outwardsfrom the light pipe and towards condensing element 308. One example ofout-coupling layer 662 is represented schematically in FIG. 25, by meansof light pipe cross-section 710 and illustrative surface layermagnifications 712 (cross-section) and 714 (perspective view).Illustratively, left hand input ray 714 enters light pipe 654 throughface 685 and proceeds within ray segment 716, reaching layer 662 atregion 712, whose cross-section is magnified in detail 718, and whoseperspective view is magnified in detail 720. The behavior of ray segment716 depends exactly where within layer 662 the ray travels. Twoillustrative trajectories 722 and 724 are shown for generalized ray 714and illustrative micro-surface 726. Illustrative ray segment 722 strikessurface 726 of layer 662 on flat facet 728 and continues by totalinternal reflection as ray segment 728. Illustrative ray segment 724strikes surface 726 or layer 662 at tilted facet 730 and is totalinternally reflected more sharply upwards as continuing ray segment 732.Because tilted facet 730 produces so sharp an angular redirection, ray732, on reaching upper light pipe surface 705, fails the conditions oftotal internal reflection, and refracts through surface 705 asout-coupled ray segment 734.

[0267] Light pipe layer 662 can be made an integral part of either ofthe light pipe's plane surfaces (upper, 705, or lower, 707) by any oneof various methods known in the prior art including the incorporation ofa distribution of light scattering dots, prism facets, micro lenscurvatures, pyramids, straight-walled ridges, holographic opticalelements, diffraction gratings, and truncated faceted structures 740shown in FIGS. 25A-C, to mention but a few. In general, whenever a totalinternally reflecting ray such as 666 in FIGS. 22A-B hits such adisruptive feature in or on layer 662, as at illustrative point 692, theray is made to exceed the light pipe's critical angle for total internalreflection at that point, so that its re-direction and subsequentrefraction as ray 694 lies within the entrance aperture and angularacceptance range of condensing element 308.

[0268] The features of layer 662 do not convert every light pipe rayinto rays having output angles appropriate for entering condensingelement 308. Some rays miss out-coupling features and remain trapped inthe light pipe. Other rays are out-coupled, but at angles higher thanthose useful to the system. Any light pipe light that is converted tolight passing through condensing element 308, however, adds to theillumination system's efficiency.

[0269] Rays that remain trapped within light pipe 654, such asillustrative ray 696 in FIG. 22A, despite the collective actions ofout-coupling elements in layer 662, eventually return (re-cycle) tolight source array 300 for another chance. In this case, ray 696 leaveslight pipe 654 through its left hand edge face 685 as ray segment 698.Return of ray segment 698 to light source array 300 occurs via Any lightthat returns to light source array 300 may return along a quitedifferent angular path, and may actually return along more favorablepaths such as that of ray 674.

[0270] For best performance though, it is important that the featuresformed within light pipe layer 662 cause substantially more rays withinthe light pipe to enter condensing element 308 than they cause otherwisefavorable light rays from light source array 300 such as illustrativeray 674, to become unfavorable as a result of the interaction. Sincelight pipe 654 and layer 662 are positioned directly in between lightsource array 300 and condensing element 308, their collectivetransmission properties for rays such as 674 must be highly transparentand minimally disruptive to angular direction.

[0271] S. Polarization Re-Cycling and Re-Use Mechanisms

[0272] Spatial light modulators such as LCDs only make efficient use ofwell-polarized light. (Note: The metallic micro mirrors in DMDs makeefficient use of un-polarized light.) With LCDs, less than one-half theun-polarized light output from LED light source array 300 passingthrough the input aperture of condensing element 308 (as in theinventions of FIGS. 13, 15A-E, 17, 18 and 22A-B) is used effectively.Increasing the LCD's utilization efficiency of this light requires acorresponding means of converting some fraction of the light in theunused polarization state into light polarized in the orthogonalpolarization state accepted by the LCD.

[0273] One mechanism for such polarization re-cycling was describedpreviously in the inventions of FIGS. 5A-C and FIG. 11 for an LED lightsource array in which reflective polarizing layer 84 was used inconjunction with polarization conversion layer 86 just above bin array82 (or just above prism sheets 159) to cause the effective recycling andre-use of light. In this first example, polarization recycling,conversion, and re-use have been arranged entirely within the confinesof the metallic reflecting bin structure forming the array plus theprism films directly above. One linear polarization state is transmittedas output; the other, blocked by reflection, converted by phaseretardation and reflection, and ultimately recycled by reflection.

[0274] There are a number of other ways for achieving efficientlypolarized output light by locating some elements of the samepolarization recovery process external to the multi-layered light sourcearray itself, as in FIGS. 15A-E, 17, 18, and 24-26.

[0275] T. Reflective Polarizing Layer Moved to LCD Input (as in FIGS.15A-E, 17 and 18)

[0276] One such way has been anticipated in the illumination systeminventions of FIGS. 15A-E, 17 and 18. The polarization changing andrecycling layers 84 and 86 may be moved to the input aperture of LCD 306with practically the same beneficial gain in polarized output lumens. Tosee this through one example, suppose initial output rays 354 and 356 inFIG. 15A are un-polarized. Quarter-wave phase retardation layer 86 andreflective polarizer 84 (located just before LCD output aperture 304),separates condensed and un-polarized ray 356 into orthogonal linearpolarization ray components, p-polarized output ray 358 and re-cycleds-polarized return ray (which becomes left hand circularly-polarized(LHCP) ray 360 on returning back through converting layer 86. LHCPreturn ray 360 then passes back through condensing element 308 (forexample, a lens) and into light source 300 as return ray 362. Onceinside the reflective structure of light source 300, the LHCP componentray 362 converts on an odd number of metallic reflections, to theorthogonal circular polarization state, RHCP, which ultimately passesefficiently through output layers 86, 84 and 306 in the same mannerdescribed previously.

[0277] This same external polarization recovery mechanism also appliesto the higher angle light rays such as 334 and 338 that are processed(as described above) by metallic hemispherical reflector 332. When a raysuch as 338 is first emitted, it is un-polarized, and thereforeundergoes no polarization change on reflection at point 536 onhemisphere 332. When a ray such as 338 results from the return processof a LHCP ray such as 360, however, rays reaching external metallicreflector 332 convert to the orthogonal state of circular polarization.

[0278] U. Reflective Polarizing Layer Moved to Condenser Input (as inFIG. 26)

[0279] Another way to return and re-use the portion of LED output lightin the unacceptable linear polarization state is shown schematically inFIG. 26. In this particular variation on the inventions of FIG. 13 andFIGS. 15A-E, the metallic hemispherical reflector 802 is reversed in itsorientation (relative to that in FIG. 15A for example), increased inradius and used only for the collection and return of unacceptablypolarized light. Hemispherical reflector 802, shown as one example, mayalso be a generalized conicoid.

[0280] Described schematically in FIG. 26, reflective polarizing layer84 is located just below condensing element 308, and quarter-wave phaseretardation layer 86, just at the output aperture of light source array300. By this arrangement, one initially un-polarized output ray 804(shown double-lined after the convention of FIG. 11) is emitted from thecenter point of light source array 300. Illustrative ray 804 remainsun-polarized and generally unaffected by its passage throughquarter-wave phase retardation layer 86. Yet when 804 reaches reflectivepolarizing layer 84 just below condensing element 308 it splits bydesign into its two orthogonal linear polarization components (s and p),s-polarized ray 806 (shown dotted after the convention of FIG. 11)reflecting downwards towards the left hand portion of hemisphericalmirror 802 at point 808, and p-polarized ray 810 transmitting outwardsthrough reflective polarizing layer 84 and condensing element 308towards LCD 306 at edge point 812. When s-polarized ray 806 reflects atplane reflective polarizing layer 84, it does so with a predictableangle to the surface normal set by the angle between un-polarized ray804 and the surface normal to the aperture plane of light source 300.When ray 806 reaches hemispherical reflector 802 at point 808, it isreflected without polarization change back towards the hemisphericalfocal point deliberately positioned at point 814, the center point ofLCD 306. With hemispherical focal point set deliberately at point 814,reflected ray 816 must reflect back along its original path set by ray806, towards reflective polarizing layer 84, and then by reflection,back along the path of the original output ray 804, this time ass-polarized ray 818, through quarter-wave phase retardation layer 86 andinto the depths of light source 300 from whence it came.

[0281] When an un-polarized ray such as ray 804 passes through phaseretardation layer 86, its passage has no net effect on its state ofpolarization. Any linearly polarized ray component such as s-polarizedray 818 passing through this element, however, changes the ray's stateof polarization from linear to, in this case, left hand circularpolarization. Beyond this, the handedness of any circularly polarizedray (i.e. left or right) reverses on each metallic reflection that itmakes. Whenever an odd number of metallic reflections are made withinlight source array 300 and prior to departure through phase retardationlayer 86, the converted output ray resulting reverses from left handcircularly polarized (LHCP) to right hand circularly polarized (RHCP).Accordingly, any so-converted circularly polarized rays passing backthough phase retardation layer 86 converted to their correspondinglinear polarization state and therefore can transmit outwards throughreflective polarizing layer 84.

[0282] The result of this polarization recycling and conversion processis a useful one from the standpoint of power gain and efficiency only ifthe resulting p-polarized rays are generated with angular directionsfalling within the angular (and spatial) aperture of condensing element308. If they do fall within this range they will, as describedpreviously, be conveyed to LCD 306 within its acceptable angular range,and thereby increase the projection system's overall illuminationefficiency.

[0283] V. Simultaneous Polarization and High-Angle Recovery (as in FIG.27)

[0284] The invention of FIG. 26 only provides for light in thepotentially wasted polarization state to be recovered and re-used. Nocomparable means are provided, as in FIGS. 15A, 17 and 18, to recoverand re-use the otherwise wasted high angle light.

[0285] A practical means for recovering both components of wasted light(i.e. unusable polarization and unusable angle), however, is describedschematically by the cross-section of FIG. 27.

[0286] In this variation of the instant inventions introduced above, thelocations of reflective polarizing layer 84 and quarter-wave phaseretardation layer 86 remain the same as in FIG. 26, but nowhemispherical reflecting mirror 802 is converted to flat version 850comprised of metallic reflecting rings in much the same manner as wasdescribed previously (see 386 in FIG. 17). In this case, each reflectingring comprises a continuous circular reflecting facet (circular aboutsystem axis of symmetry 841) whose center of curvature is fixed on LCDcenter point 814. As such, the treatment of illustrative rays 804, 806,816, and 818 is much as described above in FIG. 26, and the contributionto polarization recovery therefore much the same.

[0287] Yet, because of reflecting mirror 850's flat configuration, highangle rays produced wastefully by light source array 300 (e.g. rays 840and 844), previously dispersed by the curved surface of hemisphericalreflecting mirror 802 in FIG. 26, are now free of all obstructions (suchas the reflector's curvature) that might otherwise inhibit the abilityto re-direct rays in more useful directions. For this purpose, a secondcollecting mirror 370 is added, made in the same form describedpreviously in FIG. 17, with each reflecting ring's radius centered asbefore, on light source 300's center point 384. Consequently, all highangle rays that are re-directed by 370, whether un-polarized orcircularly polarized, return to the aperture region of light source 300for further re-processing, and do so along substantially the same (ifnot exactly the same) paths they arrived on. The metallic reflectingrings of element 370 have no effect on the polarization state (or lackof) of the linearly polarized light rays or the un-polarized light raysthey receive and re-direct. Only circularly polarized rays reachingelement 370 have their handedness reversed; and the positioning of phaseretardation layer 86 directly above light source 300 makes this outcomeunlikely.

[0288] In this manner, reflecting element 850 processes all light raysreflected to it by layer 84, whereas reflecting element 370 process alllight rays remaining outside the respective collecting apertures ofcondensing element 308 and reflective polarizer layer 84.

[0289] In one example of this dichotomy, consider the case ofun-polarized ray 844. This ray is turned back in direction by reflector370 towards the aperture of light source 300 from whence it came as ray846, without change in polarization. As such, ray 844 and its extension846 are given another chance to be output by light source 300.Additional reflections within light source 300 may change the ray'sultimate output direction to one falling within the range of reflectinglayer 84 (e.g. a direction similar to that of ray 804). Whenever thishappens, the p-polarized component of this recovered energy passesoutwards through the system, and the s-polarized component is recycledin the same manner as rays 816, 806 and 818.

[0290] In another example of this dichotomy, consider the case of ans-polarized (rather than un-polarized) ray such as 818 returning tolight source 300 by the cooperative actions of elements 84 and 850.Suppose internal reflections with reflective array elements of 300causes eventual re-output in a ray direction similar to or in-betweenthose of wider-angle rays 840 and 844. Such rays are returned to lightsource 300 for another chance at conversion as above, with onestipulation. Their polarized energy remains trapped in multiplereflections between elements 84, 850 and 370 unless reflections (andconversions) within light source 300 results in the collective re-outputof p-polarized light having angles relative to system axis 841 nogreater than that of boundary ray 843.

[0291] As first applied in the invention of FIG. 17, the facetedreflecting rings of element 370 receive un-polarized high angle lightrays, leaving conversion to useful angles and polarization up tointernal mechanisms entirely within light source 300.

[0292] W. Generalization of Illumination Recovery and Re-Use (as inFIGS. 28A-E)

[0293] The recovery and re-use mechanisms embodied in the basic lightsource array inventions of FIGS. 3A-B, 5A-E and 11, as well as in thebasic projection system illuminator inventions of FIGS. 13, 15, and17-27 are applied as means of decreasing the system's opticalinefficiency, and not as means to reach the theoretical efficiencylimit. As will be shown further below, fundamental laws and geometricrelationships govern the maximum possible light conversion efficiencywithin given spatial, angular, polarization and wavelength constraints.

[0294] The present inventions compromise optical efficiency to achieve ahigher density of LED's within a given light source array such as 300.The methods summarized in FIG. 28A are introduced to reduce the degreeof efficiency compromised.

[0295]FIG. 28A serves as a schematic cross-section generalizing thebasic inventive elements introduced thus far, with FIGS. 28B-Esummarizing the compatible LED light sources that can be used. Lightsource 300, in this view, is a two-dimensional array of LED elementsdistinguished by use of discrete LED chips disposed within contiguousreflecting cavities (or bins) whose tapered reflecting sidewalls haveprimarily a metallic specularly reflecting behavior. While the taperedsidewalls can also be created by the total internal reflection thatoccurs at a dielectric-air boundary layer, this format achieves somewhatlower net optical efficiency than metallic boundaries (due to failure oftotal internal reflection at some angles and lack of a polarizationconversion mechanism) and is not as preferable in applications requiringhighest output efficiency. Some specific examples of light source 300are suggested in details 880 in FIGS. 28B-E. FIG. 28B represents thebasic two-dimensional reflective bin structure introduced in FIGS. 3A-B,5A-E, and 11 as layer 82. Angular recycling is added via hemisphericalreflector 862. FIG. 28C summarizes the prism sheet recycling approach ofFIGS. 3A-B, 5A-C and 11. FIG. 28D indicates that while the array of binsin detail 880 may be preferable in some situations, the use of a singlebin containing one or more LED chips is also possible, with angularrecycling added by reflecting element 862 or the addition of prismsheets. FIG. 28E represents a discretely packaged type of commerciallyavailable LED (such as the Luxeon™ emitter manufactured by LumiLeds) andis used singly or in an array. While offering less favorable performancegains than the compact LED bin arrays of FIG. 28B, arrays formed ofdiscretely packaged devices function similarly, either with anglerecycling prism sheets above them, or by themselves in concert withhemispherical reflecting element 862.

[0296] In general perspective, the inclusion of polarization recoveryrequires a minimum of 3 cooperating elements: a reflective polarizinglayer (84 in FIGS. 3A-B, 5A-C, 11, 15A-E, 17, 18, 23, 26 and 27; 872 or874 in FIG. 28A), a quarter-wave phase retardation layer (86 in FIGS.3A-B, 5A-C, 11, 15A-E, 17, 18, 23, 26 and 27; 870 in FIG. 28A) and atleast 1 (or any odd number) of metallic reflections prior to efficientoutput. Reflective polarizing layer 84, 872 and 874 appears as apolarization selective mirror plane that separates un-polarized lightinto its two orthogonal linear polarization states (s and p) byreflecting one and transmitting the other. Such materials aremanufactured using polymers preferably by Minnesota Mining andManufacturing Company (3M), under the trade name, DBEF™. Quarter-wavephase retardation layer 86 is preferably a thin polymeric film material,one useful example manufactured by Nitto Denko. These films, whenoriented appropriately with respect to the polar axis of the linearpolarized light passing through them, cause efficient conversion fromlinear polarization to circular polarization.

[0297] Numerous examples of the polarization recovery process usingthese elements have been given above. The purpose of FIG. 28A, however,is to show within a single schematic, a graphic summary of all thevarious angle and polarization recovery responsibilities.

[0298] Illustrative output ray 890 emanates from the left hand edge ofplanar light source 300. This illustrative ray is directed with themaximum angular extent permissible by the aperture conditions ofcondensing element 308. When this ray is p-polarized by re-cycling andpolarization conversion processes are within light source 300 there isno need for further processing, except by condensing element 308, whichre-directs the ray as continuing segment 892 to LCD 306. If ray 890 wereun-polarized leaving light source 300, further external processing stepsare introduced to recover or re-use a fraction of what would beotherwise wasted polarization. Such recovery steps involve apolarization converting element 872, placed just below condensingelement 308 or, alternatively by an equivalent converting element 874placed just below LCD 306. In either case, the converting element (872or 874) is composed of a reflective polarizer layer that reflects onelinear polarization state and transmits the orthogonal state. Acooperating quarter-wave phase retardation layer 870 is located justabove light source 300.

[0299] As one example of this configuration, converting element 872 ispresumed in position just below condensing element 308. As such, element872 serves to split un-polarized light ray 890 at point 906 into its twoorthogonal linear polarization states, p-polarized ray 892, transmittedand processed by condenser 308, and s-polarized ray 896, reflecteddownwards towards reflective element 864 and target point 905 onreflective element 864.

[0300] When s-polarized ray 896 reaches reflective element 864 it isreflected symmetrically and without change in polarization about line903 extending from point of reflection 905 to center of curvature 814.As a result, reflected ray segment 902 heads back towards point 909 onconverting element 872, which it sees as mirror plane 908. Consequently,s-polarized ray 902 is redirected as s-polarized ray 904 back towardslight source 300, and the region of its right most edge. As ray 904passes through quarter-wave phase retardation element 870 itspolarization converts from linear to circular. This conversion step iscritical to the instant inventions herein as it enables the metallicreflections occurring within light source 300 to effect changes inpolarization. Without such polarization changes, there would be nopossibility of polarization recovery and gain. Re-emitted output raysfrom light source 300 remain s-polarized, and thereby unable to passthrough converting element 972. Such rays remain trapped reflectivelybetween element 972 and light source 300. Only by means of polarizationchange are these rays able to escape entrapment, as potentially usefulcontributions to output.

[0301] As another example, converting element 872 is positioned justbelow LCD 306. In this case, illustrative un-polarized ray 890 isredirected towards LCD 306 by condensing element 308 as un-polarized raysegment 892. When ray 892 reaches converting element 872, it immediatelysplits into transmitted p-polarized output ray 894 and back-reflecteds-polarized ray 898. S-polarized ray 890 is directed downwards, backthrough condensing element 308 and through phase retardation element 86,onwards into light source 300. Once again, effective reuse of thisrecycled energy depends on the polarization conversion process:conversion of s-polarized ray segment 900 by element 86 into itscorresponding circular polarization state and subsequent conversion tothe orthogonal circular polarization by metallic reflection.

[0302] Two external ring-segmented reflecting elements are involved inthe recovery processes. Disk-like element 864 surrounds light source 300and its circular reflecting rings redirect rays reflected towards it byconverting element 872 when it is located below condensing element 308.Cylindrical element 861, whose axis is concentric with symmetry axis901, also surrounds light source 300, and redirects light rays emanatingfrom it, regardless of polarization state, that are not otherwisecollected and used by condensing element 308. It is applied as a meansof recovering and reusing high angle light rays that would otherwiseescape the system.

[0303] Disk-like ring-segmented hemispherical reflector 864 is designedin conjunction with converting element 872 so that its focal point 814is folded by mirror plane 908 to coincide with center point 384 of lightsource 300.

[0304] Cylindrical ring-segmented hemispherical reflector 862 isdesigned to return high-angle light rays, whether they are polarized orun-polarized. Focal point of reflector 862 is also made to coincidecenter point 384 of light source 300.

[0305] X. Illuminator Performance, the Fundamental Geometric Limit andSpatial Character of Arrays

[0306] Ultimate performance of LED illuminators such as have beendescribed in the sections above, and regardless of their application, islimited by a fundamental geometric invariant known as etendue.Assessments of performance are best made in relation to designs thatoperate at or near this theoretical limit. While the geometric invariantapplies to individual LED illuminators and arrays of individual LEDilluminator elements alike, a distinguishing feature of the presentinventions is the way in which they capitalize on the collectiveperformance of array elements. That is, the spatial overlap or sharingof output light between neighboring LED array elements found to be acritical contributor to the collective performance achieved.

[0307] As a deliberate starting point, the instant inventions of FIGS.3A-B, 5A-C, 11, 13, 15A-E, 17, 18 and 22-28 were not constructed topreserve etendue from aperture to aperture throughout their opticalsystems. Starting with the LED source aperture etendue limits areequated by the Sine Law (A_(i)×Sin²θ₁), relating the net etendue ofevery i^(th) aperture. Designs preserving etendue are constrainedgeometrically, a consequence, in geometrically constrained applicationsas projection display, that could restrict suitability. Plus, withetendue preserved, no further optical output gain is allowed (within anygiven polarization state or wavelength) by the re-cycling and re-usemethods that have been incorporate above.

[0308] Re-cycling and re-use as applied herein, reduces the amount bywhich the otherwise non-etendue preserving designs fall short of thefundamental geometric limit. The more re-cycling and re-use that isincluded, the closer output performance can come to that associated withthe geometric limit—without exceeding it.

[0309] Moreover, the particular mechanisms of recycling and reuse imparta degree of spatial de-localization that contributes to the array'sspatial uniformity and enhances its overall performance efficiency.

[0310] Y. Etendue-Preserving Reflector Array (as in FIGS. 29A-B)

[0311] The etendue-preserving version of the instant inventions is shownin both the schematic cross-section 910 of FIG. 29A and in theperspective view 916 of FIG. 29B, illustratively, for a 9-element array.Each contiguous etendue-preserving bin 913 is designed with a minimum of4 reflecting sidewalls 912, the shape of each which variesmathematically as described by prior art in such a way that the Sine Lawis preserved between input 100 and output 914 apertures. The same LEDchip 118 as has been described above is placed within input aperture 100of each bin. The well-known Sine Law determines the minimum size of theoutput aperture, X_(o), 914, by equation 7, where X_(i) is the inputaperture size and θ_(o) is the maximum output angle. LED 1 18 ispresumed to emit over the full ±90-degree hemisphere, but other morelimited angular emission ranges are just as easily accommodated by meansof equation 7.

X _(o) =X _(i) Sin 90/Sin θ_(o)   (7)

[0312] The structure of FIG. 29A-B is best suited for those illuminationapplications where highest possible efficiency is critical andcompactness constraints on illumination aperture 914 are sufficientlymodest. Video projection systems, such as those described by theinvention of FIG. 13, have been shown to impose very strict boundaryconstraints on illuminator size. One illustration of this restriction isoffered for a maximum preferable illumination angle of ±25-degrees inair (±16.48-degrees in encapsulating media of refractive index 1.49), inconjunction with a 1.2 mm (diagonal) LCD (or DMD) video image source andf/2.4 projection optics. Under these conditions, the maximum permissibleilluminator size becomes, by the geometry of FIG. 13, 12 mm×12 mm.Suitability of the bin array depicted in FIGS. 29A-B depend ondetermining just how many of its ideally designed bins (and LEDs) fitwithin the geometry-limited aperture. Using 1 mm×1 mm LED chips arrangedto fit exactly within input aperture 100 of each reflecting bin 913(X_(i)=1) and bins filled with dielectric material 911 of refractiveindex 1.49 rather than air, its seen from equation 7 that X_(o)=3.53 mm.Accordingly, for X and Y-meridian symmetry, we find that only eleven3.53 mm×3.53 mm bins fit within the 12 mm×12 mm illumination aperture.With each 1 mm green LED emitting a maximum of 100 lumens/mm², themaximum output power per bin array 910 is therefore 1,100 un-polarizedlumens, which after allowances for realistic reflection losses andabsorption falls to about 900 lumens.

[0313] Judging suitability under these conditions depends on the targetprojector's total lumen need. Today's commercially competitive frontprojector products using conventional discharge lamps deliver more than1,000 white-field lumens on-screen. It was shown earlier that to achievethis performance level at least 1,600 un-polarized green lumens must berealized within the illustrative ±25-degree angular range from all binsfitting within the corresponding 12 mm×12 mm aperture. While this outputlevel has been offered by the less-efficient non-etendue-preservinginventions of FIGS. 3A-B, 5A-C, 11, 13, 15A-E, 17, 18 and 22-28, thereis a 1.6× shortfall using the more efficient etendue-preserving array ofFIGS. 29A-B.

[0314] The primary reason for this shortfall is that the Sine Lawpreserving design of bins 910 achieves high efficiency at the expense ofreduced lumen density. The primary reason the non-etendue designssucceed is that they achieve elevated lumen density at the expense ofefficiency.

[0315] Z. Genus of Non-Etendue-Preserving Reflector Array (as in FIGS.29A-B-FIGS. 30A-B)

[0316] Circumventing theoretical limits without violating fundamentallaw begins by compromising on efficiency. Designing to reach the SineLaw's theoretical limit implies 100% efficiency (prior to materiallosses).

[0317] Such inefficiency trade-off is precisely the genus of thenon-etendue-preserving inventions of FIGS. 3A-B, 5A-C, 11, 13, 15A-E,17, 18 and 22-28. The etendue-preserving invention of FIGS. 29A-Btransfers, before normal material losses, 100% of the emitted flux tothe angular range of interest (i.e. ±25-degrees in this example).Correspondingly, and even after benefit from the recovery and re-useinventions of FIGS. 15A-E, 17, 18, and 22-28, only about 50%-60% of thetotal emitted flux (from each LED) is expected to transfer within theangular range of interest.

[0318] The specific path of inefficiency taken is traced schematicallyin FIGS. 30A-B and FIGS. 31A-B. The evolution begins imaginarily bymoving the ideal reflecting bins of the cross-section in FIG. 29A towardeach other so that bin reflecting walls 910 overlap as indicated by thesolid lines of FIG. 30B and the dotted lines of FIG. 31B. By doing so,more bins can be fit within any given area. Of course, overlap regions922 have no optical function, and the imposing reflector sidewalls 925would drastically alter optical throughput.

[0319] The boundary between practical and impractical is indicated byline 920 in FIG. 30B and FIG. 31B. Only the non-overlapping reflectingregion drawn below line 920 is practical, but achieves practically noselective angle transformation over the range ±90 degrees. Light output924 from truncated bins 926 is essentially a Lambertian distribution.The entire reflector shape 910 is needed to impart angle transformationfrom ±90 degrees to the range of interest. Consequently, shiftingoptical power from the higher output angles to the lower output anglesrequires finding a functional alternative to upper bin portions 929 ofFIG. 30B.

[0320] One such functional alternative is provided by prism sheetstructures 92 and 88 of FIGS. 3A-B, 5A-C, and 11, as representedschematically in the light source array of FIG. 31B.

[0321] While conjunction of a specularly reflective LED bin array withover-lying prism sheets as depicted in FIG. 31 B does not achieve assharply a confined angular output as do the deeper bin array of FIGS.29A-B, it does achieve a much more favorable non-Lambertian outputdistribution, FIG. 31 A, than do the truncated bins 926 of FIG. 30B usedalone, which develops the Lambertian distribution of FIG. 30A. Truncatedbin array 926 establishes lumen density, and cooperating prism sheets 88and 92 facilitate the angular redistribution process. The new outputdistribution 928 shows significantly increased output within angularrange of interest 922 at the expense of reduced output at higher outputangles. The angular redistribution process implicit in such light sourcearrays involve the reflective recycling mechanisms discussed above, aswell as a unique interaction between the design variables of thereflecting bins 926 (depth and sidewall slope) and those of the prismsheets 88 and 92 (prism angle, refractive index, and elevation above theLEDs 118).

[0322] In addition, there is another unique characteristic of thenon-etendue-preserving bin arrays of FIGS. 31A-B. Light generated by anyone bin in the array spreads by the recycling process to neighboringbins. Because of the fixed tightness of the array, this spatialspreading only dilutes lumen density at the array boundaries, whileconstant lumen density is maintained within the array by spatialsuperposition. This important characteristic of the present inventionswill be described in more detail further below.

[0323] AA. On the Degree of Theoretical Inefficiency

[0324] The etendue-preserving bin array of FIGS. 29A-B achieves themaximum geometric efficiency allowed by thermodynamic law. Thenon-etendue-preserving designs of FIGS. 3A-B, 5A-C, 11, 13, 15A-E, 17,18, 22A-28A, and 31A-B have purposely sacrificed this efficiency todevelop higher lumen density. The degree of inefficiency involveddepends on the details of the embodiment.

[0325] A convenient way to characterize inefficiency ofnon-etendue-preserving arrays is to consider the array as a singleentity and contrast its performance with a single etendue-preserving LEDsource of the same total emitting area. For the 40-bin, 9 mm×12 mm LEDarray example used frequently above, with 1 mm LEDs emitting 100 lumensover ±90 degrees from dielectric to air, the equivalent LED source areais that of the 40 LEDs themselves, or 40 mm². The geometrical limit theninsists that the Sine Law product of the array be less than theeffective source product, which is (40^(0.5)) (Sin 25)/(1.49) or 1.79.

[0326] The fundamental source density has been consciously diluted inthe array inventions of FIGS. 3A-B, 5A-C, 11, 15A-E, 17, 18 and 22A-28A.The illustrative 40-bin array involves 40-mm² of LEDs spread over the72-mm² array's aperture. Consequently, there is a corresponding loss tothe fundamental (efficiency) limit. With 40 identical 1.6 mm bins, theloss to the fundamental limit reduced to 1.6²/1.0² or 2.56. Thisdeliberate inefficiency allows considerable margin for the re-cyclingand re-use inventions of FIGS. 3A-B, 5A-C 11, 15A-E, 17, 18, 22, 2326-28B and 31A-B to improve output performance - and do so without anyviolation of fundamental law.

[0327] Simply, there is no violation of law unless it can be shown thatsome combination of mechanisms lead to a system aperture brightnessexceeding that of the fundamental source.

[0328] The inventions of FIGS. 3A-B, 5A-C, 11, 13, 15A-E, 17, 18, 22, 2326-28B and 31A-B retreat from the geometric limit at ±90 degrees bydispersing the source (array) over a larger aperture than requiredtheoretically. While the selective re-cycling and re-use mechanisms thendecrease this initial inefficiency, their constructive actions neverreach the theoretical limit.

[0329] The flip-chip LED configurations described by FIGS. 6A-C aresurrounded in a transparent dielectric medium (rather than air) toextract the maximum possible emitted flux. For this reason, such LEDsare better suited to the non-etendue-preserving illumination systems ofFIGS. 3A-B, 5A-C, 11, 13, 15A-E, 17, 18, 22, 23 26-28B and 31A-B than toideal etendue-preserving system of FIGS. 29A-B, at least for theprojection system embodiments of FIGS. 15A-E, 17, 18, and 22-28B thathave particularly tight illumination aperture constraints.

[0330] In projection systems, as mentioned earlier, etendue is driven byspatial and angular constraints on its image aperture 306 (LCD or DMD).Critical elements include physical area and maximum permissibleacceptance angle. The fundamental light source used might typically belarger and thereby contain more geometric limit than can be usedeffectively. The digital micro mirror device, also known as a DMD (ordigital light processor, DLP™), has micro mirrors that are deflectedelectronically through a maximum angle of 24 degrees. Most commercialmicro-sized LCD contrast ratios fall significantly at illuminationangles beyond ±12 degrees.

[0331] The impact of such constraints is more apparent by an earlyprojection system example. Additional examples will be introduced insection 6 below.

[0332] AB. Projection System Example

[0333] The effect of such constraints on projection system efficiency isillustrated by the following example for the illustrative 4:3 imageaperture 306 of 446 mm² (1.2″ diagonal with 4:3 aspect ratio). Thisimage aperture supports a maximum illumination angle of +/12 degrees inair. Accordingly, the effective geometric limit becomes (446)(Sin² 12)or 19.28. Condenser element 308, as in FIG. 13, converts light fromlight source 300 within a chosen angular range (i.e. +/25 degrees) tothe specific angular range (±12 degrees in air) handled effectively bythe imaging device 306. This means that the overall illuminationaperture area at ±25-degrees, A₂₅, cannot exceed its Sine Law equivalentthrough the equality, (A₂₅)(Sin² 25)=(446)(Sin² 12). So, maximumeffective illumination area A₂₅ is 107.9 mm².

[0334] The non-etendue-preserving illuminator arrays of FIGS. 3A-B,5A-C, 11, and 31A-B are restricted to this area, but contain 40 mm² ofLEDs whose output, while boosted in the range of ±25-degrees, spreadsover ±90-degrees.

[0335] This result is related to the geometric ideal by determining theLED aperture at ±90-degrees that, converts all LED emission to the sameangle (±25-degrees) and aperture (107.9 mm²)—as by the idealized binstructure of FIG. 29. This ideal LED emitter has an aperture(107.9)(Sin² 25/n²), A_(LED)=8.68 mm² with n=1.49. This hypothetical LEDcorresponds to about 9 individual 1 mm² chips packed tightly together asa 3 mm×3 mm composite.

[0336] Hence, the higher lumen density achieved with thenon-etendue-preserving approach over the etendue-preserving approachclearly stems from its use (and powering) of 4.6 times more LEDs. Forexample, using 40 green LEDs at 100 lumens/mm2 per LED, in the 1.6mm×1.6 mm optimized reflecting bins of FIG. 7, contributes about 1000un-polarized lumens to image aperture 306. Adding optimized prism sheets88 and 92 as in FIGS. 3A-B, 5A-C 11 and 31A-B increases lumen use to1550 (practically the 1600 un-polarized lumen required from thisdiscussion above for a 1000 white-field lumen front projector).

[0337] As re-cycling is made more efficient, and as the angle-changingmechanisms associated with re-use efficiency improved, still furtheradvances in illuminator performance are permitted without penalty.

[0338] AC. Aperture Brightness Perspective

[0339] Yet another way of looking at the difference between the twotypes of light source arrays introduced above is in terms of theircomparative aperture brightness. The fundamental brightness of a 40 mm²LED source aperture at an LED performance level of 100 lumens/mm² is9,290,000 FL (foot-Lamberts or FL). Yet, the act of spreading these same40 LEDs and their ±90-degrees of angular emission over the largeretendue-preserving aperture of chosen angular range (i.e. ±25-degrees),dilutes this fundamental full angle brightness spatially by a factor of1/(1.62) or 2.56 to 3,628,906 FL. Then, by virtue of the angulardiscrimination imparted by condenser element 308 (as in the imageprojection system of FIG. 13), only about ±25 degrees of this LED'sangular emission is redirected to image aperture 306. Such angulardilution, if not tempered in some way, further reduces aperturebrightness (i.e. by Sin²(25) from 3,628,906 FL to 648,145 FL). Therecycling and reuse mechanisms embodied in the instant inventions ofFIGS. 3A-B, 5A-C, 11, 13, 15A-E, 17, 18, 22, 23, 26-28B and 31A-B actexplicitly to reduce angular dilution. One example is taken from FIG. 7,with 1550 lumens achieved in ±25-degrees over an aperture of 102.4 mm².This performance corresponds to an aperture brightness of 1,406,247FL—about twice the fully diluted brightness achieved using conventionaltechnology. While a doubling of performance is significant, there isstill considerable room for additional improvements without violation offundamental law.

[0340] AD. LED Arrays and Spatial Overlap of Output Light

[0341] A critical facet of the performance character of illuminatorarrays of the present inventions relates to the nature of opticaloverlap achieved between physically distinct array elements.

[0342] The spatial distribution of output light immediately above anarray of LEDs enclosed in physically distinct reflecting bins, cavitiesor compartments is composed of a corresponding array of contiguous oroverlapping light patterns generated at and beyond the output aperturesof the entire array from the performance due to any one LED element ofthe array turned on and all the others turned off. The collectivesuperposition affects output efficiency and spatial uniformity. Inaddition, when the LEDs in the array represent more than one emissioncolor, the collective superposition affects color homogeneity as well.

[0343] AE. Output of Etendue Preserving Arrays: FIGS. 32A-B

[0344] The simple output light composite pattern 1050 of a 3×3 array ofetendue-preserving bins as formed in FIGS. 29A-B is shown schematicallyin FIG. 32A with the central unit 1052 on (white) and the 8 surroundingbins off (black). Output light is confined spatially to physicalaperture 1054 of the bin whose LED is activated. For a 100 lumen LED,about 93 lumens are output within the angular range designed. Equallysimple output light pattern composite 1056 of the same 3×3 array ofetendue-preserving bins is shown schematically in FIG. 32B with all 9LEDs turned on (white). In such cases, the output light from thecomplete array becomes a contiguous representation of the light patterndeveloped at the output aperture of any representative bin unit in thearray operating alone. In such cases, the array's lumen density (inlumens/mm²) is defined by lumen density at the output aperture of anyarray element. Output light is confined to square boundaries 1058 of theetendue-preserving bin's output aperture—which for an illustrative±30-degree design is 3 mm×3 mm. So for this 3×3 array, the overall areaof contiguous elements is 9 mm×9 mm.

[0345] When polarization recycling re-cycling elements 84 and 86 areincluded in the array, as in FIGS. 29A-B, light emitted by any or allgiven bins within the array re-cycle to and are re-emitted byneighboring bins, creating a situation of spatial light spreading andoverlap such as described just below. In this case, lumen densityresults of the same spatial overlap that is a more important fundamentalcharacteristic of the non-etendue preserving arrays.

[0346] AF. Output of Non-Etendue-Preserving Arrays: FIGS. 33A-B.

[0347] The spatial light spreading that occurs in thenon-etendue-preserving illuminator inventions of FIGS. 1A-3B, 5A-C, 11and 31A-B is shown schematically in FIGS. 33A-B for a 3×3 array ofcontiguous 1.6 mm square bins 82 (one 100 lumen LED per bin), bin array82 covered by two prism sheets 88 and 92 containing preferably104-degree prisms. The total lumen output from any given bin within theillustrative ±30-degree angular range is about 50 lumens. Detail 1060 ofFIG. 33A is a topographic map showing exactly how these lumensdistribute spatially in percent among the nine contiguous 1.6 mm binsinvolved. Map 1060 is formed for the special illustrative case when theLED in central bin 1062 is on, and all surrounding LEDs are off. Forthis case, about 76% of the total lumens within the ±30-degree angularrange specified, or about 38 lumens, remain confined to the 1.6 mmsquare aperture area of central bin 1062.

[0348] A perspective view of bin array 82 and prism sheets 88 and 92 isshown in detail 1064 of FIG. 33B, so as to illustrate more clearly theeffective light spreading involved. Spatial overlap of output light toneighboring bins is a deliberate feature of the illuminator inventionscombining bins and prism sheets, bins and polarization re-cycling, orboth. In the simple case of bins and prism sheets, the spreading toneighboring bins is a feature brought about specifically by the opticalinterplay between elevated prism sheets 88 and 92 and the underlyingreflecting bins 82, as discussed earlier. The extent of the spreading iscontrolled by prism sheet elevation 102, G1, above the LED array itself,plus geometric parameters of the prism sheets used.

[0349] Detail 1060 in FIG. 33A is representative of the characteristicspatial output pattern observed both experimentally and with thecomputer model described earlier. The four nearest neighbor bins 1066,1068, 1070, and 1072 about central bin 1062 each contribute about 4% ofthe lumen total. The four next-nearest neighbor corner bins 1074, 1076,1078 and 1080 each contribute 1% of the lumen total.

[0350] Yet another perspective on the bin array's light spreadingcharacteristic is given in FIG. 34, which plots the fraction of totaleffective lumens that are enclosed within progressively larger squaresabout central bin 1062 as a function of the size of the squaresconsidered. In this context, effective light is that light containedwithin the specified angular range, either ±25-degrees (triangles, Δ) or±30-degrees (squares, □).

[0351] The numeric data represented in FIGS. 33A-B and the graphic datarepresented in FIG. 34 are directly related. The number of lumenscontained within 1.6 mm×1.6 mm central bin 1062 in FIGS. 33A-B isrelated by dotted line 1082 in FIG. 34. Similarly, the number of lumenscontained within the 3×3 array's 4.8 mm×4.8 mm boundary, as in FIGS.33A-B, is related by dotted line 1084 in FIG. 34.

[0352] AG. Third Form: Deeper-Profile Multi-Layer LED Arrays UsingShaped-Wall Reflecting Bins

[0353] The third form of the present invention, introduced previously inFIGS. 29A-B, B, features an LED light source array composed ofcontiguous reflecting bins 910 whose curved sidewalls 912 have beenshaped to preserve etendue from LED input aperture 100 to angle-limitedoutput aperture 914. An optional polarization recovery and reusemechanism has been added by elements 84 (reflective polarizer) and 86(quarter-wave phase retardation film) for applications needing polarizedlight. This compact array design is distinguished by its contiguous binstructure and in polarization-sensitive applications like LCD videoprojection, by its metallic sidewalls 912.

[0354] Despite the etendue-preserving array's remarkable brightnessefficiency, the bin geometries impose fundamental limit on the number ofoutput lumens that can be achieved per square millimeter. Best useapplies to applications needing to maximize lumens per watt.

[0355] AH. Performance of an Etendue-Preserving Light Source Array

[0356] Suppose etendue-preserving reflecting bins 910 of FIGS. 29A-Bcontain, as described above, 1 mm green LEDs capable of emitting 100lumens at 50 lumens/watt in 1 mm square input apertures 100. Eachdielectrically filled bin has an output aperture edge size of 3.53 mm,and a length, L, 909, (X_(o)+X_(i))/2 Tan θ_(o)=7.67 mm, for outputlight at ±25-degrees. Only 11 such bins fit in theprojection-system-limited (12 mm×12 mm) illumination aperture at±25-degrees. Accordingly, this design yields 880 lumens at 22 watts (40lumens/watt), including realistic material loss.

[0357] The non-etendue preserving multi-layered LED light source arraysof FIGS. 3A-B, 5A-C, and 11, with illustrative 1.6 mm bins fits about 56bins in the same aperture area and yields 38.3 lumens per bin over thesame angular range. This corresponds to a total output of over 2,000lumens at 112.5 watts (19.4 lumens/watt).

[0358] It is clear than the etendue-preserving design of FIGS. 29A-B hasa decided efficiency advantage, using 5 times fewer watts (and LEDs)over the same aperture. At the same time, the etendue-preserving designyields 2.5 times fewer lumens. Matched to the same aperture and lumens,the etendue-preserving design uses half as many watts as thenon-etendue-preserving approach with half as many LEDs.

[0359] AI. Efficient Polarization Recovery and the Etendue-PreservingLight Source Array

[0360] The LCD micro displays used in video projection systems such asdescribed in FIGS. 13, 15A-C, 18, 22, 23, 26-28B used only polarizedlight. When un-polarized illumination is directed to their inputapertures, half the light is discarded (either by absorption orreflection). A key aspect of the present invention has been includingillumination processes that recover, convert, and re-use some portion ofthis otherwise wasted light.

[0361] One means of polarization recovery are films 84 and 86 in FIGS.29A-B as described earlier. High efficiency is possible because of theparticularly straightforward relation between films and metallic bins,along with the relatively few return cycles needed before recycledoutput is achieved.

[0362] An example of this process was discussed earlier. In summary,un-polarized LED light ray 1000 passes through the bin's dielectric fillmaterial 911 and reflects from right hand sidewall 912 at point 1002.After reflection reflected ray 1004, remaining un-polarized, passesthrough quarter-wave phase retardation layer 86 with no effect andstrikes reflective polarizer 84 at point 1006. With films 86 and 84properly oriented with respect to each other, linearly polarized outputray 1008 is p-polarized, and linearly polarized reflected ray 1010 iss-polarized. When s-polarized ray 1010 passes back through phaseretardation layer 86, its polarization state is converted from linear toleft hand circular, as has been well established in prior art, and inprevious examples above. So-converted, left hand circularly polarizedray 1012 passes back (in this one example) into the same bin from whichit came, reaching left hand sidewall at point 1014, where it isconverted again to right hand circularly polarized ray 1016 andspecularly reflected downwards towards the LED at bin bottom point 1018.In this case, illustrative bottom point 1018 is the LEDs undersidemirror. Accordingly, incoming ray 1016 is converted on reflection at1018 back to left hand circular polarization as out-going ray 1020.Out-going ray 1029 reaches bin sidewall 912 at point 1022, and onreflection, converts back to right hand circular polarization, as ray1024.

[0363] In the above sequence, circularly polarized rays madepolarization-converting metallic reflections three times at points 1014,1018 and 1022. Because of the odd number of metallic reflections, thestate of circular polarization changed from the left-handedness ofincoming ray 1012 to the right-handedness of out-going ray 1024.Accordingly, bin output ray 1026 converts from right hand circularpolarization to linear p-polarization on passing back through phaseretardation layer 86, and thereby, also through reflective polarizer 84as p-polarized output ray 1028.

[0364] In this manner, the total amount of p-polarized light isincrementally increased. If bin sidewall reflectivity is R_(BIN), LEDmirror reflectivity, R_(LED), phase retardation layer transmissivity,T_(QW), reflective polarizer reflectivity, R_(RP), and reflectivepolarizer transmissivity, T_(RP), an estimate can be made of thepotential polarization recovery gain. In this case, very few of theFresnel reflections are actually lost completely from use. So, ignoringFresnel reflections for convenience, it can be shown that thepolarization recovery gain, η, is approximated by equation 8 below.Moreover, since output light is contained within a reasonably narrowangular range (the illustrative ±25-degrees), transmissivity andreflectivity performance of wide band reflective polarizer 84 are higherthan in the LCD backlighting applications for which they were firstdeveloped. With R_(BIN) set at 0.95, R_(LED) at 0.85, and R_(RP) at0.94, the estimated polarization recovery gain, η, becomes approximately1.75.

η=1+(R _(BIN))²(R _(RP))(R _(LED))   (8)

[0365] This analytical estimate was verified by actual laboratorymeasurements of polarization gain in a metallic reflecting system usinggreen LEDs manufactured by LumiLeds, silver coated electro-formed nickelreflecting bins, wide band quarter wave phase retardation filmmanufactured by Nitto Denko and the reflective polarizer known as DBEF™manufactured by 3M. The Nitto Denko phase retardation film was actuallylaminated to the DBEF using a non-birefringent pressure sensitiveadhesive, and positioned as shown in FIGS. 29A-B, just above outputapertures 100 of light-emitting bin array 910. Output light wascollected through the 1″ diameter entrance port of a 48″ in diameterintegrating sphere manufactured by Labsphere, Inc. An absorptionpolarizer was used to verify the linear polarization of the resultingoutput light. Measurements were made with and without the laminated filmpack in place. Without the film pack, output light remainedun-polarized. With the film pack in place as shown, measured output waslinearly polarized. The measurement of gain ratio involved the polarizedlight output with film pack in place divided by half the measured amountof un-polarized light without the film pack. Gain measurements variedbetween 1.7 and 1.75, depending on reflector quality.

[0366] AJ. Practical Aspects of Fabrication and Assembly

[0367] Critical material elements of the instant inventions includedherein are the metallic reflecting bin arrays (element 12 and 22 inFIGS. 1A-B, element 60 in FIGS. 2A-C, element 82 in FIGS. 3A-B, 5A-C and11, element 126 in FIG. 4A and element 910 in FIG. 29A), the LED chip(element 20 in FIGS. IA-B, element 70 in FIG. 2, element 118 in FIGS.3A-B, 5A-C, 6, 11, 19-21 and 29A-B), prism sheets (elements 4 and 6 inFIGS. IA-B, elements 88 and 92 in FIGS. 3A-B, 5A-C, 11, 20 and 31B),polarization recovery films (element 28 in FIGS. 1A-B, element 56 inFIG. 2, elements 84 and 86 in FIGS. 3A-B, 5A-C, 11, 15A-E, 17, 18, 23,26 and 27, and elements 870 and 872 in FIG. 28A) and conicoidal(hemispherical or ellipsoidal) collecting mirrors (element 332 in FIGS.15A-E and 16, element 382 in FIG. 17, element 394 in FIG. 18, element650 in FIG. 22A-B, element 802 in FIG. 26, elements 370 and 850 in FIG.27, and elements 862 and 864 in FIG. 28A).

[0368] AK. Fabrications and Processing of Critical Parts

[0369] All critical parts are either available commercially, or havebeen fabricated using existing commercial infrastructures. Theinformation provided below is for purposes of illustration only. Moresuitable materials and processes are likely to develop over time.

[0370] AL. Metallic Reflecting Bin Arrays

[0371] The generalized non-etendue-preserving bin arrays shown in theperspective view of FIG. 4A have square (or rectangular) symmetry. Whileanalogous circular and hexagonal structures are permissible, the square(or rectangular) forms of FIG. 4A are the most straightforward, andmatch the shape of current LED chips. Such structures are formed usingconventional form tool 128 or in materials like silicon compatible withcrystallographic-based reactive ion etching. Conventional tool masterssuch as element 128 in FIG. 4B are cut or ruled in a relatively softmetal such as copper or nickel using pre-shaped diamond cutters. Themaster tool (a negative pattern) is then copied by nickelelectroforming, in two well-known process steps (first making thepositive structure, and then electroforming the positive to make thenegative copy). The negative tool copy is then used repetitively to makethe desired bin arrays. These arrays can be based on the nickelelectroforms themselves, or the tool copy can be used to emboss or moldthis pattern into a high temperature resistant polymer. In either case,the as-formed bin array sidewalls 106 are then coated with ahigh-reflectivity metallic film (i.e. silver or aluminum), by vapordeposition (evaporation, CVD, or sputtering) or electroplating.

[0372] One additional complication of the electroforming process is thatit doesn't provide intrinsically for the clear holes needed in each binelement from input to output aperture. The excess nickel electroformmaterial must be physically removed by cutting, grinding or polishing,just to the top of the tool mesas 129 as in FIG. 4B. This extra step isnot necessary when molding casting or embossing a polymer (orglass-polymer alloy), as double-sided tooling is a practicalconsideration.

[0373] When forming metallic parts, the backside of the array (i.e.nearest the LED) is insulated with a layer of photo-resist, spun onglass, silicon dioxide, aluminum oxide or other non-conductor.

[0374] The same methods are used to form the deeper etendue-preservingbin arrays of FIGS. 29A-B.

[0375] AM. LED Chips

[0376] The instant light source array inventions depicted by FIGS. 3A-B,5A-C, 11, 29 and 31A-B are best embodied with flip-chip LEDs as havebeen described earlier, because the flip-chip mounting style facilitatesmaking electrical interconnections. The older vertical-junction-typeLEDs requires one connection on the chip bottom, and another on the chiptop (usually a gold wire bond). Although planar methods have beendescribed for avoiding top-of-chip wire bonds, they introduceconsiderable assembly process complexity.

[0377] Another advantage of the flip-chip format is that it enablesusing a highly reflective underside mirror (element 125 in FIG. 6B).Manufacturers making LEDs without this feature may not be able toachieve as high a level of luminous flux (lumens) as does LumiLeds withtheir Luxeon™ styled 1 mm and 2 mm flip-chips. Moreover, using LEDswithout underside mirror 125 within present light source inventionsreduces illuminator efficiency primarily by reducing the effectivenessof angular and polarization recycling processes. As one example or this,consider right hand circularly polarized ray segment 1016 in FIG. 29A.Without mirror 125 being a part of LED chip 118, not only would there bevery little energy in reflected ray 1020, but there would be noeffective polarization conversion at point 1018. Without polarizationconversion occurring at point 1018, this illustrative component ofrecycled energy would remain trapped within the light source.

[0378] AN. Prism Sheets

[0379] The prism sheets preferred for best mode results using theinstant inventions of FIGS. 1A-3B, 5A-C, 11 and 31B are those, asdescribed above, whose 25-100 micron sized micro-prisms nominallycontain 100-108-degree apex angles, and that have been formed using anon-birefringent optically transparent polymeric material.

[0380] Ordinary commercially available micro-scale prism sheets are madewith only 90-degree prisms, and may involve additional modifications(peak rounding, prism rounding, and diffusing substrates, as well asdeliberate prism height and prism pitch variations) added forperformance enhancements in the direct view LCD display applications forwhich they are intended. Minnesota Mining and Manufacturing Company (3M)produces such materials under a variety of BEF-related trade namesincluding BEF, BEF II, BEF III-M, BEF III-T, RBEF, WBEF and morerecently, under the general envelope of Vikuiti™, both sold as displayenhancement products specifically for directly viewed LCD panels. BEF IIis supplied with 24 and 50-micron 90-degree prisms, BEF III with 50micron 90-degree prisms. M designates a matt or diffusing substrate, T,a transparent substrate.

[0381] In addition to providing less preferable prism geometry, all3M-made film products have intrinsic birefringence, which limits theirperformance in applications of the present inventions involvingpolarized light.

[0382] AO. Polarization Recovery Films

[0383] Polarization recovery films include a reflective polarizing film84 and a quarter-wave phase retardation film 86, either separately or asa laminated pair or pack.

[0384] The best commercially available reflective polarizers are thosesupplied by 3M under the trade names DBEF and DBEF M for dual brightnessenhancement film with and without a diffuser, and DRPF for diffusereflective polarizer film. For use as element 84, the DBEF product ispreferred. All reflective polarizers 84 include a designatedpolarization axis that, for best results with the present light sourceinventions, must be oriented at or about 45-degrees to the designatedaxis of quarter-wave phase retardation film 86.

[0385] The best quarter-wave phase retardation films for use as element86 are those supplied by Nitto Denko. These are pre-stretched polymerfilms with a designated alignment axis.

[0386] AP. External Mirrors

[0387] A variety of conicoidal reflectors have been described, whoseshape is either hemispherical, cylindrical with hemispherical reflectingrings, cylindrical with rings containing corner cube retro-reflectingelements, or ellipsoidal. These elements can be made by a wide varietyof conventional forming processes including numerically controlledmachining, fly cutting, molding, casting and electroforming, to give afew examples. The elements can be made from a continuous piece ofmaterial (metal or plastic), or can be formed in sections that are latersnapped, soldered or glued together. Forming in sections is mostconvenient for the cylindrical geometries (i.e. half cylinders).

[0388] AQ. Integration and Interconnection of LED Chips

[0389] The instant LED light source array inventions of FIGS. 1A-3B,5A-C, 11, 29A-B and 31A-B require making electrical interconnection tothe positive and negative sides of as few as 1-9 high-power LEDs, and asmany as 64. This means assuring not only proper voltage drop across eachdiode (nominally about 3 volts; typically 2.5-3.5 volts), but also themeans for the maximum current flow required (nominally 0.667 amperes forthe higher operating power possible in the near future (typically 0.35amperes to 0.700 amperes).

[0390] Generally, there are four regimes of practice: providing aseparate constant current source for each LED; wiring all LEDs inseries, wiring all LEDs in parallel, and some practical combination. Themeans of incorporating these different wiring arrangements will beillustrated below for the two prevailing interconnection possibilities:individually sub-mounted LED chips, and all LED chips in the arraymounted to a common substrate circuit.

[0391] AR. Interconnection of Separately Sub-Mounted LED Chips (as inFIGS. 35A-E and FIG. 36)

[0392] Commercially-available high-power flip-chip LEDs, such as thoserepresented in FIGS. 6A-C, are currently pre-mounted (i.e., by LumiLeds)mirror 125 side down on silicon substrate circuits 112, with accessiblepositive and negative electrode pads 116 and 114 as the externallead-outs from the proprietary solder-bump electrical interconnectionsmade under LED chip 118 to mirror electrodes 125.

[0393] Using individually pre-mounted structures is possible, asrepresented schematically in FIGS. 35A-E, although doing so is generallyinconvenient particularly for large LED arrays, since this correspondsto twice the effort. For small arrays, the method of FIGS. 35A-E ismanageable, but for the relatively large (i.e., 6×8) arrays illustrated,a two-step interconnection process is much more labor intensive thannecessary.

[0394] The method of FIGS. 35A-E was first introduced in principle bythe cross-section of FIGS. 3A-B, where LED chip 118 was inserted throughinput aperture 100 of reflecting bin layer 82, so that its LED sub-mount112 makes physical and electrical contact with the underside of binarray sidewall structure 105. FIG. 35D is an illustrative top view ofthis bin array layer back plane. If bin layer 82 is made of anelectrically conductive material such as nickel or silicon as describedpreviously, its backside (diagonally ruled) must be insulated with athin non-conductive over coating such as for example, photo-resist,silicon dioxide, aluminum dioxide or a spin-on-glass 1150. If bin layer82 is made of a suitable high-temperature polymeric material such as athermo set resin, no secondary-insulation layer 1150 is necessary.

[0395] In either case, a thin-film electrical circuit layer 1152 isdeposited or printed as shown, so that a particularly then means isprovided for electrically conductive interconnection to sub-mountedelectrode pads like 114 and 116 on each pre-mounted LED as in FIGS.35A-C. The use of conventional gold wire bonds would restrict the degreeof physical proximity possible between bin array 82 and LED sub-mount112. Best performance by the instant inventions and their previousdescriptions, require the bottom of the LED's physical substrate to bemade as close to co-planar with bottom surface 1154 of bin arraysidewall structure 105 as possible.

[0396] Ordinarily, a convenient way to form such a thin delineatedprinted circuit is by means of photolithography. In such a case, and toavoid the possibility of short circuits between the conductive filmmaterial and the conductive bin array material (if it is conducting), itis best that the conductive circuit elements such as 1156 are madephysically narrower than the insulated space upon which they are to beformed. There are several common photolithographic means to achieve thiscondition, including the lift-off process wherein photo-delineatedphoto-resist is over-coated with a vapor-deposited gold film. Afterdeposition, the photo-resist is dissolved, and the unwanted gold iscarried away leaving the desired conductive pattern. Thickness of thegold conductors can be increased to several microns by subsequent goldelectroplating. At least 2 microns of conductor thickness are preferredso as to accommodate the high electrical power levels involved.

[0397] A schematic cross-section of the LED insertion process is shownin FIG. 35E. Two illustrative reflecting bins are shown incross-section, with an LED 118 about to be inserted downwards into theright hand bin, and another LED already properly inserted downwards intothe left hand bin's aperture. It can be seen that LED sub-mount contactpads 114 and 116 touch the bin arrays adjacent conducting bars 1156.

[0398] AS. Sub-Mount Styles: FIGS. 35A-C

[0399] LumiLeds Luxeon™ sub-mounts 112 are currently hexagonally shaped,with positive pad 116 and negative pad 114 relative to the hexagonalpoints 1160 and 1162 as in 1169 of FIG. 35A. Equally feasible is squaresub-mount 1164, as in upper center 1170 of FIG. 35B, and hexagonalsub-mount 112 with opposing contact pads 114 and 116 relative to twoopposing hexagonal edges 1166 and 1168 as in upper right detail 1172 ofFIG. 35C.

[0400] In any case, compatibility with the array inventions of FIGS.1A-3B, 5A-C, 11, 29A-B, and 31A-B requires the maximum size of sub-mount112 to be adjusted so that it is less than or equal to the pitch of thearray. In the example above for non-etendue-preserving shallow bin lightsource arrays illustrated in the cross-section of FIG. 5A, thereflecting bins are 1.6 mm square and arranged contiguously. As such,compatible LED sub-mounts must be just less than 1.6 mm. If sizecompatibility is not considered, sub-mounts 112 in FIGS. 35A-C could notbe placed on the bin array plate of FIG. 35D without physicallyinterfering with each other.

[0401] AT. Interconnection Circuitry on Bin Array Bottoms: FIGS. 35D-E.

[0402] The illustrative electrical circuit shown in FIG. 35D for a 6×8bin array is composed of 9 parallel (electrically conductive) buss bars:1176 for positive voltage, 7 thinner bars like 1156, and ground bar1152. This particular circuit connects all 6 LED sub-mounts in any ofthe 8 rows in parallel, and then the six rows in series. The LEDsub-mounts in any column would therefore be oriented p-n, p-n, p-n, p-n,p-n, p-n, p-n, p-n, and p-n from top to bottom; and in any row, eachdiode would have identical orientation. Another related interconnectionscheme is shown schematically in FIG. 36 in which each set of twoadjacent LED sub-mounts in every row are connected in parallel.

[0403] AU. Interconnection of LED Chips on a Common Back Plane Circuit:FIGS. 37-38.

[0404] A better way of interconnecting an array of LED chips 118 for usein the instant inventions herein is to arrange the LED chips 118 in rowsand columns on a common back plane circuit such as 1200 as depictedschematically in the top view of FIG. 37. The individually sub-mountedLEDs are sawed from a larger silicon wafer to which they have beenpermanently attached. Rather than perform this extra cutting step, eachmaster silicon wafer can be arranged with larger regions 1200 ofproperly oriented interconnection pads for the flip-chip LEDs in eacharray. Then individual array regions 1200 can later be sawed from themaster wafer rather than the individual chips. The silicon wafer hasbeen pre-oxidized to provide insulating barrier layer 1202 between thesilicon itself a semiconductor, and over-lying conducting circuitelements 1152, 1176 and 1204. Oxidized silicon layer 1202 is preferredin that it minimizes the chances of leakage paths through thesemi-conducting silicon for the high current levels flowing in theelectrical circuitry. As in FIGS. 35D and 36, the black bars correspondto photo-delineated conducting films (i.e. vapor or electrodepositedgold). In the illustrative circuit of FIG. 37, LED chips 118 placed in 6columns on the 6×8 array shown in this particular illustrative view,wired in series from positive supply buss conductor 1176 to electricalneutral or ground buss 1152. Individual interconnection bars 1204straddle each two adjacent LED chips 118. Upper and lower buss bars 1176(upper) and 1152 (lower) assure that the 6 columns are connected inparallel.

[0405] Yet another circuit arrangement beyond those examples in FIGS.35-37 is provided in FIG. 38, in which all 48 LED chips 118 areconnected in parallel. The conductive circuit that achieves this type ofinterconnection is the well-known inter-digital electrodes used in manytypes of electronic devices. One advantage of its use herein is that thevoltage-drops across each LED in a column are equivalent. This isbecause the sum of the lengths of inter-digital conducting bars 1210 and1212 from source buss to any particular LED in a column is alwaysconstant.

[0406] Each LED chip in the array is attached to the conductive circuitby the same solder-bump process used currently by manufacturers offlip-chip products like LumiLeds, as symbolized in FIGS. 35D-E and 36.

[0407] The principal advantage of this interconnection method is thatany reflecting bin array 82 such the one shown by partial perspective inFIG. 4A can be simply over-laid on the common back plane, even by hand.The only requirement for the success of this assembly step is that eachLED must have been placed onto element 1200 within the rather widetolerance allowance provided by each bin's slightly over-sized inputaperture. As shown in the cross-sectional details of FIGS. 3A-B, 5A-Cand 11, bin aperture X_(i) 100 is made deliberately larger than LED chipsize X_(c), 97 (as in FIGS. 3A-B) by some practical amount (i.e.,X_(i)=1.1 X_(c) or X_(i)=1.05 X_(c)).

[0408] The principal drawback of the common LED back plane 1200 is thatevery LED chip 118 bonded to it must be functioning properly (or atleast within acceptable limits) for the array to perform satisfactorilyin any given application. The use of individually-sub-mounted LEDsallows, in principal, for each device element to be checked forperformance prior to its attachment to element 1200.

[0409] While some means of testing can be developed for the bare LEDchips, prior (and even during) the process of attaching them to thearray, it is important to realize that within the instant inventionsherein, it is not essential for every LED chip 118 in the array toperform either identically or even similarly. That is, the use of thenon-etendue-preserving instant light source inventions of FIGS. 1A-3B,5A-C, 11 and 31A-B as integrated by the system inventions of FIGS. 13,15A-E, 17, 18, 22A-23B and 26-28E provides sufficient spatial averagingin the output beam conveyed to (and through) output aperture 304, thatless than ideal LED array uniformity is tolerated. Moreover in theillustrative 48-element arrays of FIGS. 35A-38, the completelyunsatisfactory performance of even 5 devices, worst case, reducesexpected output lumens by only 10% (or less).

[0410] AV. Special Applications in LED-Based Video Projection

[0411] The LED light source inventions described above apply to twodifferent classes of video projection system application: those drivenby total lumens regardless of power efficiency of light source arrays ofFIGS. 1A-3B, 5A-C, 11 and 31A-B) and those lower-powered designs drivenby the higher wattage efficiency of light source arrays of FIGS. 29A-B).

[0412] Although some useful examples have been given along the way inthe course of the discussions above, it serves in summary to contrastthe differences between these two commercially important applicationregimes. Before doing so, however, the underlying geometricalrelationships common to both regimes are summarized for convenience.

[0413] AW. Geometrical Relationships in Preferred LED-Based ProjectionSystems (as in FIGS. 13, 15A-E, 18, 22, 23 and 26-28E)

[0414] A preferred arrangement for integrating the planar LED lightsource array of the instant inventions in a video projection system hasbeen generalized in FIG. 13. [The same basic principles apply to theequivalent systems of FIGS. 15A-E, 18, 22A-B, 23A-B and 26-28E.] In thisillustrative configuration, space 317 between light source 300 andcondensing element 308 is typically air, and space 319 betweencondensing element 308 and the LCD (or DMD) 306 is taken up by asystem-specific dielectric element. The form of this intervening mediumand the effective location of LCD (or DMD) 306 (as in FIG. 13 or rotated90-degrees from the position shown in FIG. 13) depend on the projectionsystem architecture. That is, when using an LCD that is reflective, theintervening medium becomes a polarizing beam splitter. When the LCD istransmissive the intervening medium may either be empty (air), or forfield-sequential applications using a single LCD, may be a dichroiccolor mixing X-cube, dichroic reflecting plates or dichroic prism group.

[0415] As one possible example common to both high lumen and low wattageoperating regimes, a single transmissive LCD 1400 is considered whoseswitching speed has been made fast enough for practical field sequentialoperation (i.e. >180 Hz). In this case, the geometry of FIG. 13 in theX-meridian becomes that of FIG. 46, wherein three separate mono-coloredillumination channels (1404, green; 1402, red; and 1406, blue) surroundthe three adjacent sides of a color-mixing element (in this casedichroic X-cube 1364). Color mixing element 1364 combines the threeillumination beams from each channel's condensing element 308 into asingle output beam whose angular range has been reduced to φ_(LCD) inair and φ'_(LCD) in the dielectric medium. The three planar LED lightsource arrays 300 (e.g., FIGS. 15B-E, 29A-B) are represented by 1390(green), 1388 (red) and 1392 (blue). In fact, each illumination channelconsisting of an LED light source array and a condensing element, becomelight engine cores (1404, green; 1402, red; and 1406, blue) of thehigher-level projection engine.

[0416] The first geometric design condition pertinent to FIGS. 13 and 43is described by equation 9. It represents the minimum possible focallength for condensing elements 308, as measured through the illustrativeoptical media of dichroic mixing cube 1364. This media may also be apolarizing beam splitting cube, air, a polarizing beam splitter plate,dichroic reflecting plates or group of optically coupled dichroicprisms. $\begin{matrix}{{FL}_{{MIN},{media}} = \frac{Y_{LCD}}{\left( {1 - {2\quad {{Tan}\left( {{Sin}^{- 1}\left( {{1/2}{n\left( {f/\#} \right)}} \right)} \right)}}} \right.}} & (9)\end{matrix}$

[0417] The shorter edge length of the LCD, Y_(LCD), is that whichextends into the x-meridian planes of both FIGS. 13 and 46, n is therefractive index of X-cube 1364, and f/# refers to the acceptance anglein air of projection lens 1362.

[0418] When the projection system's f/# is 2.4 (i.e. ±12-degrees as inthe above examples), refractive index 1.49, and a 1.2″ diagonal LCD 1400with 4:3 aspect ratio is used, the minimum focal length caused by themixing cube medium (i.e., 310 in FIG. 13, 1364 in FIG. 46) becomes 25.49mm. A corresponding expression for the minimum focal length in air onthe light source side of the light engine (i.e., 311 in FIG. 13) isgiven by equation 10. $\begin{matrix}{{FL}_{{MIN},{air}} = {\frac{0.5\quad X_{ILL}}{{Tan}\quad \varphi_{LCD}^{\prime}} = \frac{0.5\quad X_{LCD}}{{Tan}\quad \theta_{ILL}}}} & (10)\end{matrix}$

[0419] For the same conditions, this back focal length 311 is 16.9 mm.With the focal lengths fixed at their physical minimums, calculation ismade of the maximum possible illumination aperture, X_(ILL), 302 in FIG.13, using equations 9 and 10 to form equation 11. $\begin{matrix}{X_{{ILL},\max} = \frac{2Y_{LCD}{Tan}\quad \varphi_{LCD}^{\prime}}{\left( {1 - {2\quad {Tan}\quad \varphi_{LCD}^{\prime}}} \right)}} & (11)\end{matrix}$

[0420] It follows that X_(ILL, max) is 7.2 mm, which might be consideredtoo small for some applications. If so, the illumination aperture may beincreased progressively by just increasing the system's focal length, asby the simple geometry of equation 12, where focal length and LCDaperture angle are both either in air or in media. Of course, by doingso, the effective illumination angle, θ_(ILL), decreases proportionally.

X _(ILL,extended)=2(FL)Tan φ_(LCD)   (12)

[0421] For example, suppose the system's focal length and the size ofmixing cube 1364 in FIG. 46 were increased to 41 mm (a size increase of1.6×). By equation 10, this change corresponds to a lower side focallength in air of 27.18 mm. Then, by equation 12, the illuminator size302 in FIG. 13 that results has expanded to 11.58 mm. At the same time,equation 10 shows that the effective illumination angle, θ_(ILL), dropsfrom its X and Y meridian values in air of ±35.82-degrees and±28.42-degrees (average ±32.12-degrees) before the focal lengthincrease, to ±24.16-degrees and ±18.59-degrees (average ±21.36-degrees)after the change. Whether the tradeoff between system size, illuminatorsize and illumination angle is worthwhile depends on making detailedanalyses using a predictive systems model, such as the one describedabove, or performing corresponding lab experiments using real parts.

[0422] The clear aperture of condensing element 308, from the geometryof FIG. 13 is approximately equal to the corner-to-corner length of LCD(or DMD) 306 plus the corner-to-corner length, (X_(ILL) ²+Y_(ILL)²)^(0.5), of light source array 300.

[0423] The general characteristics of this invention will becomeapparent considering illustrative examples using each type of optimizedilluminator.

[0424] AX. Optimum Performance of High Output (Non-Etendue-Preserving)LED Arrays

[0425] The analyses discussed in sections A-H for non-etendue-preservingLED-filled bin arrays of the present invention are summarized by theresults of FIGS. 7-10, 12 and 14. Preference was found, in theillustrative case of 1 mm sized LEDs, for 1.6 mm square reflecting bins,0.174 mm deep, flat-tapered reflecting walls, 1 mm input apertures, andprism sheets having apex angles about 104-degrees full angle. Maximumlumen output as a function of angular range enclosed is given in FIG. 39for effective bin reflectivity 0.95, bin-fill medium refractive index,1.49, prism sheet material refractive index 1.49, and 1 mm LEDs emitting100 lumens/mm².

[0426] Curve 1214 represents the optimum result in un-polarized lumensper bin with 104-degree prism sheets 88 and 92 (i.e., without anypolarization recovery or re-use). The addition of polarization recoverylayers 84 and 86 between the prism sheets and the bin aperture resultsin polarized output approximately 1.5 times the half-values shown inFIG. 39, provided neither sheets 88 or 92 are made of birefringentmaterial or show effects of residual birefringence. Curve 1216 is theresult using prism sheets with standard 90-degree prisms. Curve 1220shows the performance from the reflecting bins by themselves without anycooperating optical over-layers. The addition of polarization recoverylayers 84 and 86 in this case results in a measured polarized output 1.7times the half-values shown in curve 1220.

[0427] The net un-polarized output contributed per bin over ±25-degreesfor the optimized case of curve 1214 is 41 lumens (point 1218); and over±30-degrees, about 52 lumens (point 1215). The comparative results forstandard 90-degree prisms are 33 and 39 lumens respectively. Hence, theadvantage of using optimized 104-degree prism sheets over 90-degreeprism sheets is therefore about 24% (over ±25-degrees) and 33% (over±30-degrees). The advantage of using optimized 104-degree prism sheetsover reflectively binned LEDs without cooperative action, over eitherangular range, is about the factor of 2 predicted in earlier analyses.

[0428] Light distribution across the aperture of anon-etendue-preserving bin array develops by means of the spatialoverlap mechanism described in FIGS. 33A-B for the case of singlelighted bin 1062 surrounded by 8 unlighted neighbors. FIG. 40 is a topview of an analogous representation of light output over 64-bin array1250 when all array elements are lighted. The percentage value showncentered within each bin region corresponds to the bin's net outputfraction produced within the angular range of interest (in this case,±25-degrees). These values already take into account the inherentinefficiency of the non-etendue-preserving process displayed in FIG. 39,which at ±25-degrees is about 40% of the total lumen output per bin.Average output from the 64-bin array aperture 1252 is 90% of the totallumens produced, from the output ratio[(36)(0.94)+(24)(0.86)+(4)(0.81)]/[64]. This means that with 40 lumensproduced by each of the 64 bins, 2,300 lumens are generated within a±25-degree beam.

[0429] The schematic representation of FIG. 40 directly illustrates thedegree of spatial non-uniformity occurring across the array's physicalaperture 1252, X_(ILL). This characteristic is not so important ingeneral lighting applications where some intensity roll-off at the beamperiphery is even desirable. Beam uniformity, however, it is a veryimportant contributor to the brightness uniformity of projected images.

[0430] Spatial non-uniformity in this illustrative beam occurs only inthe beam periphery. The dark-toned frame of weak output in FIG. 40corresponds to lumens displaced outside physical illumination aperture1252. While such wasted light is not desired, its existence does notaffect the quality of the light source array's projected output. Onlythe physical array's 28 outermost bins show any geometricnon-uniformity, and that, on image display industry standards, is quitemodest. The center to corner roll-off is a very respectable 0.86; andthis is before any deliberate system averaging occurs within the focalplane projection systems of FIGS. 13, 15A, 17, 18, 22A-B, 23A-B, and26-28A.

[0431] Non-uniformity may also arise from unintended performancedifferences between individual LEDs in the array. Manufacturing processvariation combined with electric interconnect differences may lead to arandom distribution of brightness (or lumen) variations from bin-to-bin.Fortunately, the spatial overlap process of FIGS. 33A-B also works tosoften these effects at least slightly.

[0432] When all LEDs emit identically, collective overlap fromsurrounding neighbors increase any given bin's output from 76% to 94% ofthe single bin total. Each bin's output increases by constructiveoverlap with neighbors. The 76% a given bin contributes from its ownphysical boundaries are enhanced by 4 nearest neighbor contributions of4% each, and 4 next nearest neighbor contributions of 1% each, summingto 96%. In this manner, it can be seen that about 38.4 lumens areemitted within the 1.6 mm×1.6 mm physical boundary of bin 1254 in FIG.40 (within ±25-degrees).

[0433] Suppose bin 1254 in FIG. 40 contained a low-performing LEDproducing 50 lumens/mm² rather than the 100 lumens/mm² intended. Theeffect on local uniformity of this severe perturbation is illustrated bythe graphic of FIG. 41A showing only the 6×6 inner core of the 8×8 arrayof FIG. 40. While the disturbance is concentrated in the region ofoffending bin 1254, the correspondingly smaller number of lumensoverlapping with 8 neighboring bins 1258 has a small effect on theiroutput as well. The details of this lumen distribution are shown inmagnified graphic 1260 of FIG. 41B. Because of the spatial lumen influxfrom brighter neighbors such as bin 1262, deficient bin 1254 outputs23.2 lumens rather than the 19.2 lumens expected from its half powerLED. Accordingly the overlap mechanism as shown in FIGS. 33A-B works toreduce local non-uniformity by 20%.

[0434] AY. Optimum Performance of High Output (Etendue-Preserving) LEDArrays

[0435] The output performance of the etendue-preserving designintroduced in FIGS. 29A-B is typified by curve 167 in FIG. 12. Thisideally curved bin wall was designed to output ±30-degrees into air, anddoes. As seen in FIG. 12, very little light actually extends outsidethis angular range. With 0.95 reflecting sidewalls, the highly efficientreflecting bin delivers about 93 of its 100 possible lumens within theangular range designed. In practice, curvature errors may diminish thisefficiency slightly.

[0436] Output light from the etendue-preserving array, at least in theabsence of the addition of cooperating films such as 84 and 86 of FIGS.29A-B, is tightly bound to each reflecting bin in array 910. Thislocalization is illustrated schematically by the spatial distributionsof FIGS. 32A-B.

[0437] In geometrically constrained applications like video projection,illuminator size, shape and output angle all must match the need of therectangular video display used. If the inherent geometric symmetry ofboth the bins and the array illustrated in FIGS. 29A-B are maintained,however, there will be a considerable loss in optical efficiency. Thisloss of efficiency stems from the symmetric array's inability to provideeven illumination over an asymmetric field without waste from overfill.More specifically, the contiguous array of etendue-preservingmetallically reflecting bins surrounding each square LED chip cannotprovide adequate illumination flux to the corners of rectangular LCD (orDMD) micro-displays arranged as in FIGS. 13, 15A, 17 or 18. Withoutfurther modification, the ability of such illuminators to cover arectangular field evenly requires significant overfilling of that field,as if by a circular beam, and the attendant inefficiency of so doing.The reason for this deficiency stems from the preservation of etendue ineach meridian, combined with the inviolate nature of the well-knownPythagorean Theorem which mandates the relationship between the sides ofsquare (or rectangular) elements, and their diagonal length. Thegeometry of field coverage in an image projection system has beenexplained in relation to FIG. 13 as being a consequence of theillumination angles, θ_(ILL), in each meridian. Generalized in equation10, the required illumination angles in the X, the Y and the diagonalmeridians in air are isolated by equations 13-15, where in this case, FLis the effective focal length in air or media depending on exactly whatoccupies the space between condensing element 308 and image displaydevice 306, and X_(LCD), Y_(LCD) and D_(LCD) are the respective lengthsof the rectangular image display device (either an LCD or a DMD).Converting these angle to their counterparts in bin media is Sinθ_(ILL,air)=n Sin θ_(ILL,med). Geometry dictates via the Pythagoreantheorem, that D_(LCD)=(X_(LCD) ²+Y_(LCD) ²)^(0.5). $\begin{matrix}{\theta_{{ILL},X} = {{Tan}^{- 1}\left\lfloor \frac{X_{LCD}}{FL} \right\rfloor}} & (13) \\{\theta_{{ILL},Y} = {{Tan}^{- 1}\left\lfloor \frac{Y_{LCD}}{FL} \right\rfloor}} & (14) \\{\theta_{{ILL},D} = {{Tan}^{- 1}\left\lfloor \frac{D_{LCD}}{FL} \right\rfloor}} & (15)\end{matrix}$

[0438] The implication of these geometrical relations can be understoodthrough the following example for a rectangular 0.7″ LCD 306 with 4:3edge-length to edge-width aspect ratio, as in the system arrangement ofthe instant invention of FIG. 13. The focal length, FL, of condensingelement 308 for this smaller LCD format is taken illustratively, as 12.7mm in air. For these conditions, planar illuminator 300 must provideillumination flux within ±29.25-degrees in its X-meridian,±22.78-degrees in its Y-meridian and ±34.99-degrees in itsdiagonal-meridian. If the illumination angles fall short of any of theseangular ranges, less than complete field coverage will result—producingdark shadows and/or the complete absence of image information.

[0439] The contiguous LED bin array illustrated in FIGS. 29A-B has beenconstrained by means of each bin's sidewall shape 912 to preserveetendue in each meridian. Although the Sine Law is well known andstraightforward, it is still useful to summarize the resulting outputillumination angles in each of the illuminator's X, Y and diagonalmeridians, as in equations 16-18. $\begin{matrix}{\theta_{{ILL},X} = {{Sin}^{- 1}\left\lbrack \frac{X_{LED}{Sin}\quad \theta_{{LED},X}}{X_{BIN}} \right\rbrack}} & (16) \\{\theta_{{ILL},Y} = {{Sin}^{- 1}\left\lbrack \frac{Y_{LED}{Sin}\quad \theta_{{LED},Y}}{Y_{BIN}} \right\rbrack}} & (17) \\{\theta_{{ILL},D} = {{Sin}^{- 1}\left\lbrack \frac{D_{LED}{Sin}\quad \theta_{{LED},D}}{D_{BIN}} \right\rbrack}} & (18)\end{matrix}$

[0440] Using a 1 mm square LED whose natural output spreads effectivelyover a ±90-degree hemispherical volume, it follows that X_(BIN)=1 andO_(LED,X)=θ_(LED,Y)=θ_(LED,D)=90-degrees. (For LEDs that under certaindesign and packaging conditions constrain output flux to a narrowerangular range, θ_(LED) reflects that reduced angle.) With conventionalnear-Lambertian LED emitters the etendue-preserved conditions consistentwith the geometry of FIG. 13 and equations 13-15, X_(BIN)=Y_(BIN)=3.05mm, generating in air, ±29.25-degrees in both X and Y meridians. This3.05 mm square bin has a diagonal length of 4.31 mm. As such, equation18 determines that the output angle is 13.41-degrees in the bin mediaand 20.23-degrees in air. The geometry of FIG. 13 in the diagonalmeridian through equation 15 requires an illumination angle of34.99-degrees. This means that the etendue-preserving reflecting bin,while overfilling the LCD in the Y meridian, is significantlyunder-filling in the diagonal meridian. The weakness of this conditionis that the LCD corners will be comparatively dark—as if illuminated bya nearly circular beam.

[0441] One correction path for this condition is to design thereflecting bins from the perspective of its diagonal meridian. Doing soreduces the bin diagonal's length, thereby widening its angular output.Yet while doing this, angular outputs in the X and Y meridians widensimultaneously. The net result is a roughly circular far field beamprofile that covers the LCDs diagonal, but that overfills the LCD's Xand Y edges. This overfill, leads to a waste in lumens by the ratio ofthe LCD aperture to the circular area whose diameter equals that of theLCD diagonal. This geometric inefficiency ratio, η_(GEO), is governed byequation 19 with the imaging aperture's length-to-width aspect ratio,a/b. For the case where a=4 and b=3, η_(GEO)=0.61. $\begin{matrix}{\eta_{GEO} = \frac{4{ab}}{\pi \left( {a^{2} + b^{2}} \right)}} & (19)\end{matrix}$

[0442] Yet, when the field is overfilled in this manner, the effectivebin area is reduced correspondingly, and more bins are then able to fitwithin any given illuminator area, which in turn increases netefficiency.

[0443] The bin size that achieves perfect field coverage in both the Xand Y meridians is rectangular, but under-fills along the diagonal, hasby equations 13-18 has a generalized area (AREA_(—)1) as in equation 20.$\begin{matrix}{{{AREA\_}1} = \left\lfloor \frac{X_{LED}Y_{LED}}{{{Sin}\left( {{Tan}^{- 1}\left( {X_{LCD}/{FL}} \right)} \right)}{{Sin}\left( {{Tan}^{- 1}\left( {Y_{LCD}/{FL}} \right)} \right)}} \right\rfloor} & (20)\end{matrix}$

[0444] The smaller bin-size that achieves perfect field coverage onlywithin its diagonal meridian is also rectangular, and has by equations13-18 the generalized area (AREA_(—)2) given in equation 21.$\begin{matrix}{{{AREA\_}2} = \left\lfloor \frac{{{ab}\left( {X_{LED}^{2} + Y_{LED}^{2}} \right)}/\left( {a^{2} + b^{2}} \right)}{{Sin}^{2}\left( {{Tan}^{- 1}\left( {D_{LCD}/{FL}} \right)} \right)} \right\rfloor} & (21)\end{matrix}$

[0445] This means that the net increase in lumens caused by thereduction in bin area is the ratio AREA_(—)1/AREA_(—)2, generalized inequation 22. $\begin{matrix}{\eta_{BIN} = \left\lfloor \frac{\begin{matrix}\left( {{{ab}\left( {X_{LED}^{2} + Y_{LED}^{2}} \right)}/\left( {a^{2} + b^{2}} \right)} \right) \\{{{Sin}^{2}\left( {{Tan}^{- 1}\left( {D_{LCD}/{FL}} \right)} \right)}X_{LED}Y_{LED}}\end{matrix}}{{{Sin}\left( {{Tan}^{- 1}\left( {X_{LCD}/{FL}} \right)} \right)}{{Sin}\left( {{Tan}^{- 1}\left( {Y_{LCD}/{FL}} \right)} \right)}} \right\rfloor} & (22)\end{matrix}$

[0446] For the case of a square 1 mm LED, a condensing element with 12.7mm focal length and a 0.7″ LCD having 4:3 aspect ratio, η_(BIN), becomes1.307. The net inefficiency, η_(NET), is given by equation 23, whichrepresents the product of equations 19 and 22, which for this particularcase, becomes (0.61)(1.307) or 0.797.

η_(NET)=η_(GEO)η_(BIN)   (23)

[0447] AZ. Secondary Optic Elements for More Efficient Rectangular FieldCoverage

[0448] Secondary optic elements may be added above etendue-preservingilluminators of as in FIGS. 29A-B and FIGS. 42A-B and abovenon-etendue-preserving illuminators of FIGS. 3A-B, 5A-C and 11 toimprove coverage of rectangular fields.

[0449] The etendue-preserving LED array invention of FIGS. 29A-B exhibita generally circular, or at best, elliptical, far field beam profile.This characteristic behavior has been verified, not only by means ofequations 13-23 above, but also by far field output patterns from thevalidated computer model described earlier in section C.

[0450] It follows that achieving more efficient coverage of rectangularLCD (and DMD) micro-display fields requires further means to widen thearray's angular output distribution predominately along its diagonalmeridian, while making as small a corresponding change to the angularoutput distributions along the X and Y meridians as possible.

[0451] While this enhancement is illustrated for the etendue-preservinginvention of FIGS. 29A-B, it serves equally well and in the same mannerfor the non-etendue-preserving inventions of FIGS. 3A-B, 5A-C and 11.

[0452] One appropriate angle transforming means that provides the neededmodification is an orthogonally crossed arrangement of cylindricallenses 1320 as in the exploded perspective view in FIG. 42A, or thearrays of cylindrical lenses 1322 as illustrated in the explodedperspective view of FIG. 42B. An exploded perspective view is shown foreach case, isolating on a single LED-coupled reflecting unit 910, suchas one of the 9 reflecting units shown in the array of FIGS. 29A-B. LEDchip 118 is positioned within input aperture 100 of each reflecting bin910, just as in FIG. 29A. Polarization recycling layers 84 and 86 arepositioned either just above the bin's output aperture plane 1330, orjust above the lens sets 1320 and 1322. In the case of cylindrical lensset 1320, axis 1332 of lower lens 1331 is aligned parallel withreflecting bin aperture-diagonal 1334, while axis 1336 of upper lens1337 is aligned parallel with orthogonal aperture diagonal 1339. Thesame arrangements are made with cylindrical lens array set 1322, withaxis 1344 of lens 1346 parallel to bin diagonal 1334; and lens axis 1340of lens 1342 parallel with bin diagonal 1339. In either case, theoptical power is applied predominately across the two orthogonal bindiagonals, thereby effecting angular distribution more strongly in thebin's diagonal meridians than in the X and Y meridians.

[0453] Lenses 1331 and 1337 can be either conventional bulk lenseshaving either positive or negative power, or they can be cylindricalFresnel lenses. Aspheric or holographic corrections can be made tominimize off-diagonal power contributions. Lens arrays 1342 and 1346 arelenticular arrangements of parallel cylindrical lenses, also known aslenticular arrays.

[0454] When applied an as enhancement to the angular outputcharacteristics of the non-etendue-preserving LED light source arrayinventions of FIGS. 3A-B, 5A-C and 11, the lens pairs of FIGS. 42A-B arepreferably disposed above the two prism sheets 88 and 92, thecylindrical lens axes 1332 and 1336 in FIG. 42A or lenticular lens arrayaxes 1342 and 1344 in FIG. 42B are aligned in parallel withcorresponding prism sheet diagonals (diagonal 141 of lower sheet 92 anddiagonal 143 of upper sheet 88 as in perspective view 159 of FIG. 5C).Prism sheet diagonals 141 and 143 (FIG. SC), however, need not bealigned in parallel with bin aperture diagonals 129 and 131 (FIG. 4A)for best results.

[0455] BA. Performance Comparisons Between Non-Etendue-Preserving andEtendue-Preserving Design Tracks

[0456] A performance comparison is made between non-etendue preservingLED illuminator array inventions of FIGS. 1A-3B, 5A-C and 11 andetendue-preserving LED illuminator array inventions of FIGS. 29A-B and42A-B, within a given angular range. As an example, consider the meritsof the two embodiments at ±30-degrees. The non-etendue-preserving designgenerates 51 lumens per bin before polarization recycling and conversion(point 1215 in FIG. 39). This result is for 1 mm LED chips in 1.6 mmsquare tapered reflecting bins disposed just below crossed prism sheetshaving micro-prisms with 104-degree apex angles. The comparable etenduepreserving bin design generates about 93 lumens over the same angularrange (curve 167 of FIG. 12). On a lumens per solid angle basis thiswould appear to give the etendue-preserving design as much as 1.8 timesgreater total lumen efficiency.

[0457] For highly constrained video projection systems like those ofFIGS. 13, 15A, 17, and 18, however, effective lumen utilization,explained above, also depends on lumens/mm² and the total illuminatingarea, which together determine the total effective lumens possiblethrough the system's image display aperture.

[0458] It is shown by the following examples that choosing of oneembodiment over the other depend on the design circumstances. Whenseeking to maximize lumens/mm², the non-etendue-preserving embodimentsare preferred over the more efficient etendue-preserving embodiments bya factor of 2× or more. Yet, used in applications needing highestpossible power efficiency, preferable performance is achieved with theetendue-preserving embodiments where the power-saving advantage can bealmost as large.

[0459] BB. High Power Image Projection With the Non-Etendue PreservingLight Source Array: FIG. 43

[0460] Today's best ultra-compact video image projectors weigh less than5 lbs and deliver more than 1000 white-field lumens through a projectionlens and onto a projection screen.

[0461] One of many possible compact arrangements for doing so using thenon-etendue preserving light source arrays 300 of FIGS. 3A-B, 5A-C, 11,and 31A-B is shown schematically in FIG. 43 for three reflective LCDs(as elements 1358 red, 1359 green, and 1360 blue). Separate red, greenand blue illuminator and image forming sections 1351, 1353 and 1355,each based on the inventions of FIG. 13, are used for reasons explainedearlier. This illustrative layout uses the reflective LCDs inconjunction with three separate polarizing beam splitters 1356 for acompact layout. Replacing each of the polarizing beam splitter cubes1356 with air and rotating each of the image forming sections 1351, 1353and 1354 until each LCD faces an adjacent side of dichroic color mixingcube 1364, transmissive rather than reflective LCDs can be used. Equallystraightforward arrangements exist for a single transmissive LCD drivenin color field-sequential manner, as in FIG. 46, and a DMD.

[0462] Reaching for 1000 lumen performance, the green illumination andimage forming section (1353 in FIG. 43) must contribute about 600 lumens(for a 60% green, 30% red and 10% blue mixture). This means, afteraccounting for all in-line transmission and reflection losses, that thegreen light source array 1352 must provide at least 1600 un-polarizedlumens within an appropriately contained angular range (i.e.,±25-degrees as illustrated earlier for 1.2″ diagonal, 4:3 aspect ratioLCD micro-displays and f/2.4 projection optics). The 1600 un-polarizedlumens, become 1200 polarized lumens after 50% efficient polarizationrecovery, 1080 lumens after passing condenser element 308, 1026 lumensafter passing through polarizing beam splitter 1356, 923 lumens afterreflection from a reflective-type LCD (such as a liquid crystal onsilicon, LCOS) 1359, 877 lumens after reflection by polarizing beamsplitter 1356, 710 lumens after passage through dichroic prism cube1364, and 640 lumens after image projection lens 1362. Anti-reflectioncoatings are assumed on all critical surfaces, but Fresnel reflectionsmay still account for additional loss.

[0463] Optimum results for the non-etendue-preserving light source arrayhave been summarized in FIG. 39 on a per bin basis. Determining how manybins to include in the array and the array's best shape, is aconsequence of equations 9-12 above, and the focal length chosen for thecondensing element used.

[0464]FIG. 44 is a graphical summary of the relationship betweeneffective focal length (in air) and white-field screen lumens in theimage projection system of FIG. 43. Results are based on the optimum LEDbin array performance represented in FIG. 39 for 1 mm LEDs and theprojection constraints of a 1.2″ LCD used with f/2.4 optics.

[0465] In general, as in the projection system geometry of FIG. 13, thelonger the system focal length 310 and 311, the larger the illuminationarea possible, and the smaller the effective illumination angle,θ_(ILL), 322, needed to assure complete field coverage of LCD (or DMD)306 in each meridian. At the same time, the larger the allowableillumination area becomes, the more LEDs (or bins) are needed in a givenarray 300. Increasing the LED chip size from 1 mm to 2 mm, as anexample, reduces the number of LEDs and bins, but does nothing in and ofitself to reduce the number of watts. Simply, the more squaremillimeters of LEDs operating at maximum conditions (i.e. 50lumens/watt), the more watts. There is of course a practical limit.

[0466] The first data-point in FIG. 44, 1370, stems from the minimumfocal length condition discussed above (16.9 mm in air between LEDarrays 1350, 1352 and 1354 and condensing element 308 in the system ofFIG. 43). The remaining data-points are obtained by assumingprogressively larger focal lengths, and for each ensuing focal length,calculating X_(ILL)=Y_(ILL) from equation 12, η_(ILL,X) and θ_(ILL,y)from equation 10, finding the number of polarized lumens/bin at therespective angles from FIG. 39 (halving them and multiplying by therecovery factor, 1.5), calculating the number of bins from equation 4,and calculating total effective lumens per array from the product ofaverage lumens/bin and the number of bins, where the average number oflumens is the arithmetic average of the lumen values for θ_(ILL,x) andθ_(ILL,y). Once the effective number of polarized green lumens has beencalculated, the corresponding numbers for red and blue can be calculatedfrom the representative mixture (60% green, 30% red and 10% blue)assumed herein. The weighted sum represents the total number of whitelumens produced on mixing. This number is multiplied by the relativeefficiencies assumed for transmission or reflection through the system:condensing element 308 in FIG. 43, polarizing beam splitter cube 1356,dichroic color mixing X-cube 1364, LCD 1358 (1359 or 1360), andprojection lens 1362.

[0467] The integer values adjacent to each data-point in FIG. 44 are thenumber of bins per array. Since the 1 mm LEDs used in this example areexpected to generate 100 lumens at 2 watts, the number of bins effectsthe total number of watts required. Practical considerations suggestthat about 160 watts for the three illumination sections 1351, 1353 and1355 in FIG. 43 is a reasonable limit for 1000 white-field screenlumens. If this limit were imposed, the maximum number of watts in thegreen illuminator channel would be about 80, and the number of bins,about 40. Actually, dotted indicator lines 1372 and 1374 in FIG. 44 showthat the 1000 lumen target is achievable with this design for focallengths (in air) between 22 mm and 25 mm, with as few bins as 35.

[0468] In practice, the number of bins (and therefore the number of LEDchips involved) can actually be any greater number than the targetnumber chosen, with watts reduced and focal length increasedaccordingly. For example, there is no way to arrange 40 square bins in asquare array. Practical choice is between a 6×6 array and a 7×7 array.

[0469] Many other practical high-lumen projector examples are possiblealong these same lines, whether using 1 mm LED chips, smaller ones orlarger.

[0470] BC. Special Low Power Image Projector Application of the Ideal(Etendue-Preserving) Light Source Array: FIGS. 45-46.

[0471] Many new and highly mobile video projector products becomepractical as soon as it becomes feasible to operate them on batteries.Diverse combinations of cell phone, camera, camcorder, and computerfunctions all require larger and yet convenient video viewingcapabilities. Direct-view LCDs (having 1″-3″ diagonals) are the mostcommon mobile displays used today, but have limited utility because oftheir small size. Viewing personal videos, the Internet, and computerdesktops all need larger viewing surfaces. Yet, just incorporatinglarger direct view panels within hand held mobile appliances seemsimpractical. A better solution is the convergence of micro-sizedprojection displays with the convenience of lightweight hand heldprojection screens.

[0472] Battery-powered micro-sized video projection remains animpracticality with illuminators using conventional light bulbs, butbecomes a possibility using the miniature LED light source arraysdescribed above. Not only are LEDs capable of the instant on,instant-off, switching needed, but matched with the present inventionsmay be just efficient enough to provide the lumens called for.

[0473] While a sufficient number of lumens must be supplied to achieveacceptable viewing brightness over the particular screen size chosen,these lumens must be supplied at less than a target wattage suited torealistic battery size and life. For this reason, the potentially morepower efficient etendue-preserving designs of FIGS. 29A-B and 42A-B haveinherent advantage, even with only a single reflecting element used foreach color as in the system of FIG. 43, or single transmissive elementfor each color as in the system of FIG. 45.

[0474] As one example, consider the case of a battery-powered projectorcapable of achieving at least 200 Nits brightness on a hand-held 8″×10″front projection screen, initially with no screen gain. The simplegeometry of such screen and brightness criteria means that 34.2white-field screen lumens are needed across the screen's area. Thisimplies having a green illumination channel capable of contributingabout 20.5 of the 34.2 screen lumens needed.

[0475] The starting point for this is choosing the micro-display,selecting its size, and developing the corresponding projection systemlayout. One possible layout has been illustrated previously in FIG. 43for three separate reflective LCDs 1358, 1359, and 1360 (i.e., 0.7″ LCOSLCDs).

[0476] The etendue-preserving illuminators of FIGS. 29A-B then have tobe applied within each color channel to provide about[(20.5)]/[(0.9)(0.81)(0.95)(0.9)(0.95)] or 34.6 polarized green lumens,assuming the same transmission/reflection efficiencies cited above. Thismeans there have to be 41 un-polarized green lumens within the criticalangular range chosen, as polarization recovery and reuse efficiency forthis regime is ˜70%.

[0477] With 1 mm LumiLeds LEDs emitting 100 lumens/mm² each reflectingbin used yields about 90 polarized lumens (76 polarized lumens) over theangular range designed. The question remains as to what fraction ofthese lumens can be utilized in projection.

[0478] The etendue-preserving reflecting bin has an aperture size thatdepends on the angular range emitted. Relationships between angularrange, condensing element focal length and effective illuminator sizehave been summarized in equations 9-12. The angular range provides fieldcoverage needed for the LCD at any given focal length, butsimultaneously affects illuminator size. In turn, the fraction ofemitted lumens used by the LCD depends on matching effective illuminatorsize to the system's aperture angle.

[0479] The relationship between focal length and illuminator size isgoverned by equation 10, which for an f/2.4 projection system becomes(X_(ILL)/2)/FL_(air)=Tan(12). The smaller the focal length, the largerthe effective illumination area, and the larger the number of individualreflecting bins used to create it. Yet, there is a practical lower limiton focal length, as the smaller the focal length becomes, the higher theillumination angle needed to achieve complete field coverage—andwell-designed condensing optics are limited to illumination angleswithin about ±25-±35 degrees.

[0480] An individual reflecting bin for a 1 mm LED chip has an inputaperture of about 1.05 mm (allowing for some minimal clearance).Equation 10 explains that a minimum focal length of 12.7 mm in aircorresponds to a 5.41 mm square effective illumination aperture. Thiscorresponds to an effective illumination angle in each meridian of 29.25degrees in air (19.63 degrees in bin media). Designed for this angle,the etendue-preserving bin aperture becomes 3.13 mm square. This meansthat there may be (5.41²)/(3.13²) or 3 etendue-preserving bins usedeffectively. While the lumen yield from 3 bins is allowed in principle,doing so is precluded by the physical geometry. The closest physicallypractical compromise is that of a 4-bin (2×2) array, thereby overfillingthe 5.4 mm square illumination aperture permitted. It is also reasonableto use a single 2 mm LED chip in its correspondingly larger single 6.10mm square bin (with approximate 2.05 mm input aperture). In either casethe same fraction of available lumens are coupled through the 0.7″ 4:3LCD aperture onto the screen.

[0481] When using 4 square etendue preserving bins in a contiguous array(as in the 3×3 array of FIGS. 29A-B shown in FIGS. 45 and 46), one arrayfor each color channel, 4 bins cover about a 6.2 mm square region andyield (e.g., in the green channel) a total of 360 un-polarized lumens(304 polarized lumens) into the bin's sharply constrained ±29.25 degreeangular range in the symmetrical X and Y meridians. Of these lumens,only (5.4²/6.1²) or about 79% convert within the system's f/2.4constraint and are utilized effectively by the LCD aperture. Lightemitted outside the 5.4 mm square illumination boundary and collected bycondensing element 308, develops higher angled light at the LCD than canbe handled without jeopardizing system contrast. Applying theappropriate aperture (vignettes) limits polarized lumens to 240.

[0482] There is also a potential angular inefficiency to correct for, ifhighest possible illumination in the four field corners is required.Although the 6.1 mm×6.1 mm bin array preserves etendue in the threeimportant meridians (X, Y and diagonal), the angular range along the bindiagonal is smaller than that required by the geometry of equation 10.And since the etendue-preserving design cuts off pretty sharply at itsmaximum output angle (see curve 167 in FIG. 12), additional angularcoverage along the diagonal requires higher than needed angular coveragein the X and Y meridians.

[0483] Taking this into account, the net result for a 4:3 LCD aspectratio can be shown to have 61% geometrical efficiency (rather than 79%by bin aperture size alone). Accordingly, and with this correction,there are actually (0.61)(304) or 185 polarized green lumens availablemade to the LCD at 16 watts.

[0484] Such lumen production exceeds the 34.6 polarized green lumensneeded in this example by a factor of 5.3. The 4 green channel LEDs maythen be driven to the 34.6 polarized lumens needed with about 1.5 ratherthan 8 watts at full power. This means the 200 Nit performance sought onan 8″×10″ screen is achievable with a total of 3 watts—roughly thewattage of a reasonably long-lived battery in a small-sized laptopcomputer.

[0485] Still better performance is achievable by increasing focal lengthslightly in the system layout of FIG. 45 (or FIG. 46) and adding thefield coverage invention of FIGS. 42A-B to improve angular coveragealong the field diagonal without the inefficiency of over-filling. Underthese circumstances, and de-rating for 90% transmission through each ofthe two lens elements 1391 (in FIGS. 45-46) involved in the invention ofFIGS. 42A-B, as many as 246 polarized green lumens may be available at 8watts. This improvement therefore reduces the total white-field wattageneed by 50% from 3 watts to about 2 watts.

[0486] Another means of improving performance efficiency is to use asingle rectangular LED chip in a single etendue-preserving reflector binof rectangular aperture per color channel. In this case, the LED chipdimensions are scaled to provide proper field coverage in all meridians,and cylindrical or lenticular lenses used as needed to improve fieldcoverage along the aperture diagonal.

[0487] And, other than using the illustrative three reflective LCDconfiguration of FIG. 43, it is equally practical to use the threetransmissive LCD configuration of FIG. 45, shown illustratively withoutthe use of polarizing beam splitters (as sections 1382 red, 1384 greenand 1386 blue). In addition, the same low-wattage approaches can beapplied to a single field sequential LCD 1400 configured as in FIG. 46with light from each illuminator section (1402 red, 1404 green and 1406blue) combined using dichroic color mixing cube 1364. Allowance must bemade in field sequential systems for the one-third duty-cycle availableto each primary color image. When this is done with an LCD requiringpolarized light, about 3 times as many lumens are needed in each colorchannel as with the non-switched systems of FIG. 43 and FIG. 45. Whenallowance is made for field-sequential operation with the highlyreflective and polarization-insensitive DMD, a smaller allowance isneeded.

[0488] Despite the potential cost and weight savings of a fieldsequential projection system layout, there may be applications wheretrebling wattage is impractical. In such cases, handheld projectionscreens having 2×-3× gain, can be used to compensate for the smallernumber of lumens supplied to the screen in a field-sequential system.

[0489] These particular examples are given for illustrative purposesonly, and are not meant to be comprehensive. The same approaches areapplicable other arrangements and applications of LCDs and DMDs.

[0490] While preferred embodiments of the inventions herein have beenshown and described, it will be clear to those of skill in the art thatvarious changes and modifications can be made without departing from theinvention in the broader aspects set forth in the claims hereinafter. Inparticular, the various subcomponent elements and systems describedherein, as well as their optical equivalent, can be used in combinationwith, or when operatively proper substituted for, the other elements andsystems set forth herein.

What is claimed is:
 1. An illuminating system, comprising: an electricalinterconnection plate with an array of electrically conductive circuitryarranged for interconnecting one or more LED chips to positive andnegative voltage sources; an array of LED chips, said LED chips equallysized and spaced from each other a distance S that is less than or equalto width W of said LED chip; an array of metallically reflecting binswhose center to center spacing is equal to W+S, each said bin comprisinga clear output aperture and a clear input aperture formed by one or moretapered metallically reflecting sidewalls extending between them; afirst light redirecting means disposed beyond said array of metallicallyreflecting bins that transmits light in a first angular range andreflects light in a second angular range back towards said array ofbins; a second light redirecting means disposed beyond said first lightredirecting means that transmits light in a first angular range andreflects light in a second angular range back towards said first lightredirecting means; and said array of LED chips bonded electrically tosaid array of electrically conductive circuitry on said electricalinterconnection plate, said array of metallically reflecting binsdisposed just above said electrical interconnection plate such thatevery said LED chip in said array of LED chips extends in and throughthe center of every said input aperture.
 2. The illuminating system asdefined in claim 1 wherein all said LED chips in said array of LED chipseither have both their positive and negative contacts on the samesurface or their positive and negative contacts on opposing surfaces. 3.The illuminating system as defined in claim 2 wherein all said LED chipsin said array of LED chips emit light in either the same wavelengthrange, mixtures of red, green and blue wavelength ranges, or are allwhite-emitting LEDs.
 4. The illuminating system as defined in claim 2wherein all said LED chips in said array of LED chips are made with anoptically transparent substrate in the wavelength range or rangesemitted by said LED chip.
 5. The illuminating system as defined in claim1 wherein said array of metallically reflecting bins have plane taperedsidewalls slanting at angle γ from a line perpendicular to both saidclear input and output apertures, each said clear aperture being squareor rectangular in shape and related geometrically by the expression Tanγ=(1/D)(X_(o)−X_(i))/2, where D is the depth of said array ofmetallically reflecting bins, X_(o) is the edge length of an edge ofsaid clear output aperture, and X_(i) is the edge length of said clearinput aperture.
 6. The illuminating system as defined in claim 5 whereinsaid clear input and output apertures are each sized between 1.05 and1.2 mm and 1.5 and 1.7 mm respectively on their edges, and said depth ofsaid array of metallically reflecting bins D is between 170 and 180microns.
 7. The illuminating system as defined in claim 5 wherein theedge length X_(i) of each said clear input aperture is sized byX_(i)=(f)(W), the fit factor f ranging from about 1.01 to about 1.3, fbeing the minimum factor needed to permit any said LED chip to fitthrough any said clear input aperture without mechanical interference.8. The illuminating system as defined in claim 5 wherein said array ofmetallically reflecting bins are formed in plastic, glass, ceramic,metal or composite parts by molding, embossing, casting, orelectroforming from a form-tool fashioned by diamond machining, saidtapered metallically-reflecting sidewalls over-coated with ahigh-reflectivity metal film.
 9. The illuminating system as defined inclaim 8 wherein said high-reflectivity metal film is protected silver.10. The illuminating system as defined in claim 5 wherein said array ofmetallically reflecting bins are formed by photolithographic methods ina material whose thickness approximately equals said depth of said arrayof metallically reflecting bins directly.
 11. The illuminating system asdefined in claim 1 wherein said array of metallically reflecting binsare filled with a transparent dielectric medium making optical contactwith said metallically reflecting sidewalls and with the exposedsidewalls and surfaces of said LED chips.
 12. The illuminating system asdefined in claim 11 wherein said transparent dielectric medium has arefractive index for the wavelength emitted by said LED chip in therange 1.4 to 1.65.
 13. The illuminating system as defined in claim 1wherein metallic coatings on said array of metallically reflecting binsprovides a common electrical conduction path for interconnection witheither the positive or negative side of said LED chips when said LEDchips have electrical contacts on both their upper and lower surfaces.14. The illuminating system as defined in claim 1 wherein metalliccoatings on the back surface of said array of metallically reflectingbins provides isolated electrical conduction paths for interconnectingthe positive and negative sides of said LED chips when said LED chipshave electrical contacts on the same surface.
 15. The illuminatingsystem as defined in claim 1 wherein said first and second lightredirecting means are optically transparent films or sheets whose uppersurfaces are structured with parallel and contiguous prismatic grooves,the full angle of each prism apex being a constant angle selected fromwithin the range of 88 and 108 degrees.
 16. The illuminating system asdefined in claim 15 wherein said first and second light redirectingmeans are optically transparent films or sheets whose lower surfaces arelenticularly structured with parallel and contiguous cylinder lenses.17. An optical system, comprising: a liquid crystal display device whoserectangular aperture has length L and width W; a condensing system ofeffective focal length F; a planar light source array of equal lengthand width L′ comprising a regular array of contiguous reflecting bins,said reflecting bins each comprising a clear output aperture and a clearinput aperture formed by one or more tapered metallically-reflectingsidewalls extending between them, each said reflecting bin containingone or more LED chips whose emitting surfaces protrude through saidclear input aperture; a first light redirecting means disposed beyondsaid array of reflecting bins that transmits light in a first angularrange and reflects light in a second angular range back towards saidarray of bins; a second light redirecting means disposed beyond saidfirst light redirecting means that transmits light in a first angularrange and reflects light in a second angular range back towards saidfirst light redirecting means; a first polarization converting meanscomprising a quarter-wave phase retardation film a second polarizationconverting means comprising a polarization-selective reflecting film;said condensing system, and said planar light source array orientedparallel to each other on planes orthogonal to a commonly centeredoptical axis, said LCD oriented either parallel or perpendicular to saidcommonly centered optical axis, the separation distances between saidcondenser system and each said LCD and said planar light source arraybeing approximately equal to said effective focal length F of saidcondensing system, adjusted for the actual length within the dielectricmaterial (if not air) occupying the spaces in between the elements; andsaid first light directing means disposed above said reflecting bins bya gap thickness that includes air and the thickness of said array ofreflecting bins, said second light redirecting means disposed beyondsaid first light directing means by an air gap thickness, said firstpolarization converting means disposed beyond said planar reflectingbins and said second polarization converting means disposed beyond saidfirst polarization converting means.
 18. The optical system as definedin claim 17 wherein said LED chips are attached to and interconnected byelectrically conductive circuitry on a common heat conducting substrate.19. The optical system as defined in claim 18 wherein said LED chipshave both positive and negative electrodes on the same surface plane.20. The optical system as defined in claim 19 wherein said positive andnegative electrodes behave as metallically reflecting mirrors.
 21. Theoptical system as defined in claim 18 wherein said LED chips in saidplanar light source array all have a common emitting wavelength range,have a mixture of chips, one fraction emitting in the red wavelengthrange, one fraction emitting in the green wavelength range and onefraction emitting in the blue wavelength range, or each emitting over awide spectrum of wavelengths visually equivalent to white.
 22. Theoptical system defined in claim 17 wherein said plane tapered sidewallsare slanting at angle γ from a line perpendicular to both said clearinput and output apertures, each said clear aperture being square orrectangular in shape and related geometrically by the expression Tanγ=(1/D)(X_(o)−X_(i))/2, where D is the depth of said array ofmetallically reflecting bins, X_(o) is the edge length of an edge ofsaid clear output aperture, and X_(i) is the edge length of said clearinput aperture.
 23. The optical system as defined in claim 22 whereinsaid clear input and output apertures are each sized between 1.05 and1.2 mm and 1.5 and 1.7 mm respectively on their edges, and said depth ofsaid array of metallically reflecting bins D is between 170 and 180microns.
 24. The optical system as defined in claim 22 wherein the edgelength X_(i) of each said clear input aperture is sized by X_(i)=(f)(W),the fit factor f ranging from about 1.01 to about 1.3, f being theminimum factor needed to permit any said LED chip to fit through anysaid clear input aperture without mechanical interference.
 25. Theoptical system as defined in claim 22 wherein said array of metallicallyreflecting bins are formed in plastic, glass, ceramic, metal orcomposite parts by molding, embossing, casting, or electroforming from aform-tool fashioned by diamond machining, said taperedmetallically-reflecting sidewalls over-coated with a high-reflectivitymetal film.
 26. The optical system as defined in claim 25 wherein saidhigh-reflectivity metal film is protected silver.
 27. The optical systemas defined in claim 22 wherein said array of metallically reflectingbins are formed by photolithographic methods in a material whosethickness approximately equals said depth of said array of metallicallyreflecting bins directly.
 28. The optical system as defined in claim 17wherein said array of metallically reflecting bins are filled with atransparent dielectric medium making optical contact with saidmetallically reflecting sidewalls and with the exposed sidewalls andsurfaces of said LED chips.
 29. The optical system as defined in claim28 wherein said transparent dielectric medium has a refractive index forthe wavelength emitted by said LED chip in the range 1.4 to 1.65. 30.The optical system as defined in claim 22 wherein every said planetapered sidewall slants at angle γ between 30 degrees to 60 degrees ofline perpendicular to both said clear input and output apertures. 31.The optical system as defined in claim 17 wherein said first and secondlight redirecting means are optically transparent films or sheets whoseupper surfaces are structured with parallel and contiguous prismaticgrooves, the full angle of each prism apex being a constant angleselected from within the range of 88 and 108 degrees.
 32. The opticalsystem as defined in claim 31 wherein said first and second lightredirecting means are optically transparent films or sheets whose lowersurfaces are lenticularly structured with parallel and contiguouscylinder lenses.
 33. The optical system as defined in claim 31 whereinsaid first and second light redirecting means are made free ofbirefringence.
 34. The optical system as defined in claim 31 whereinsome output light is spread over all angular directions withsubstantially greater fraction of said output light linearly polarizedand contained within said first angular range by means of cooperativeaction between said LED chips, said tapered metallically-reflectingsidewalls, said first and second light redirecting means, and said firstand second polarization converting means.
 35. The optical system asdefined in claim 34 wherein linearly polarized output light results fromthe conversion of substantially un-polarized input light emitted by saidLED chips brought on by division into light of a first and second linearpolarization state by said second polarization converting means, saidfirst linear polarization state transmitted towards said condensingelement as output and said second linear polarization state reflectedthrough said first polarization converting means and converted to lightof a first circular polarization state that is then changed to light ofa second circular polarization state by its making an odd number ofreflections with said LCD chip and said tapered metallically-reflectingsidewalls before returning back through said first polarizationconverting means and converting to light of said first linearpolarization state as an additional part of said output.
 36. The opticalsystem as defined in claim 17 wherein said condensing system is at leastone of spherical or aspherical bulk, Fresnel or diffractive lenselement.
 37. The optical system as defined in claim 36 wherein the clearaperture, CA, of said condensing element approximately equals the sum ofthe corner-to-corner length of said LCD and the corner-to-corner lengthof said planar light source array.
 38. The optical system of claim 17wherein the space between said LCD and said condensing element containsone of (a) air, (b) a block of optically transparent glass or plasticmaterial composed of two 90-degree prisms optically-coupled to eachother on their hypotenuse faces by a polarization-selective coating andone or more coatings of non-birefringent optical adhesive,non-birefringent acrylate, or UV curable epoxy, so as to form apolarizing beam splitter, (c) a block of optically transparent glass orplastic material composed of four 90-degree prisms optically-coupled toeach other on their four hypotenuse faces two different dichroiccoatings so as to form a dichroic color mixing element, (d) a group ofoptically coupled and dichroically coated prisms, and (e) amulti-layered plate tilted at approximately 45-degrees to said commonlycentered optical axis.
 39. The optical system of claim 38 wherein saidmulti-layered plate contains one or more of each of the followingparallel and optically coupled elements: (a) a thin flat glass plate,(b) a polarization-selective reflecting material, and (c) an absorptionpolarizer material.
 40. The optical system of claim 17 wherein said LCDis either (a) transmissive, or (b) reflective in its mode of operation.